New to me iOptron 150mm Mak

Discuss your 'Cats' here.
Post Reply
User avatar
Bigzmey United States of America
Moderator
Moderator
Articles: 8
Offline
Posts: 7548
Joined: Sat May 11, 2019 7:55 pm
4
Location: San Diego, CA USA
Status:
Offline

TSS Awards Badges

New to me iOptron 150mm Mak

#1

Post by Bigzmey »


Thanks to generosity of Mark (John Donne) in memory of late Henry (Hankmeister3) I am a proud owner of iOptron 150mm Maksutov-Cassegrain!
Rumak-A.jpg
Was thinking of trying out a large Mak for a while, but never managed until now. Thank You so much Mark and Henry!

As you may know most of mass produced Maks on the market are of the Gregory design, where aluminized spot on the inner face of the corrector plate serves as the secondary mirror. 150mm iOptron is of the Rumak design, where a separate secondary mirror is mounted on the inner surface of the corrector plate. This provides extra degree of freedom in configuring Mak optics. You can see the secondary glued on inside, but interestingly the corrector also has aluminized spot. Could be that they are utilizing Gregory Mak corrector blanks?
Rumak-B.jpg
Mak-Casses in general are praised for small central obstructions. For example, 150mm Orion/Synta Gregory Mak has central obstruction of ~10% by area. iOptron 150mM Rumak is a different beast with central obstruction of ~14%, same as in 150mm/6” SCT. 6” SCT baffle opening is 27mm. I could not find any info on the baffle opening for the 150mm Synta Mak, but I would assume it to be like 6” SCT. This means that both scopes were designed for use with 1.25” EPs only. I have measured iOptron 150mm Rumak baffle opening to be at least 35mm. This is close to 8” SCT baffle tube opening.

My only explanation is that iOptron 150mm Rumak was designed to be 2” EP-friendly, compromising somewhat light gathering power and contrast. It will be fun to try 2" EPs in it, so I decided to go with Altair Astro 2” prism for the first light.
Rumak-E.jpg
Interestingly, most of iOptron Rumak owners report sharp and high contrast views, which makes me think that central obstruction size is just one of many optical system parameters determining contrast, and scope performance can't be solely judged just by the central obstruction size.

iOptron Rumak comes across as a well-built instrument. It is on the heavy side at ~14lb compared to ~12lb 150mm Synta Mak and 8.4lb 6” SCT, which says quality to me. :) While it is comfortable to handle, I feel that extra pounds place it beyond your typical grab and go mount like ES twilight I or SW AZGti, but it should ride well on SW Skytee 2 and iOptron AZ Mount Pro I have.

iOptron Rumak comes with a couple of nice features including two speed focuser and metal dew shield. I would certainly put the metal dew shield to a good use, however over the years I have mastered making my own custom dew shields from craft foam sheets and prefer them over metal ones.

I saw a few discussions on forums about use of insulation to overcome slow acclimation of large Maks and SCTs. That sounds reasonable and I even purchased some of the reflective foam insulation but never got around to try on my SCTs. This seems to be as good occasion as any. I wanted to make the insulation easily removable because I saw reports of moisture getting under and causing some issues. I came out with two parts: wrap-around with holes for the finder shoe and mounting bar secured in place with Velcro strips, and dew shield covering the front portion of the OTA. The dew shield has matte black flocking inside.
Rumak-C.jpg
Rumak-D.jpg
Here is the Mak sitting alongside SV102ED on iOptron AZMP, waiting for the first light. :D
Rumak-F.jpg
Scopes: Stellarvue: SV102ED; Celestron: 9.25" EdgeHD, 8" SCT, 150ST, Onyx 80ED; iOptron: Hankmeister 6" Mak; SW: 7" Mak; Meade: 80ST.
Mounts: SW: SkyTee2, AzGTi; iOptron: AZMP; ES: Twilight I; Bresser: EXOS2; UA: MicroStar.
Binos: APM: 100-90 APO; Canon: IS 15x50; Orion: Binoviewer, LG II 15x70, WV 10x50, Nikon: AE 16x50, 10x50, 8x40.
EPs: Pentax: XWs & XFs; TeleVue: Delites, Panoptic & Plossls; ES: 68, 62; Vixen: SLVs; Baader: BCOs, Aspherics, Mark IV.
Diagonals: Baader: BBHS mirror, Zeiss Spec T2 prism, Clicklock dielectric; TeleVue: Evebrite dielectric; AltairAstro: 2" prism.
Filters: Lumicon: DeepSky, UHC, OIII, H-beta; Baader: Moon & SkyGlow, Contrast Booster, UHC-S, 6-color set; Astronomik: UHC.

Observing: DSOs: 3106 (Completed: Messier, Herschel 1, 2, 3. In progress: H2,500: 2180, S110: 77). Doubles: 2382, Comets: 34, Asteroids: 255
User avatar
notFritzArgelander
In Memory
In Memory
Articles: 0
Offline
Posts: 14925
Joined: Fri May 10, 2019 4:13 pm
4
Location: Idaho US
Status:
Offline

TSS Awards Badges

Re: New to me iOptron 150mm Mak

#2

Post by notFritzArgelander »


Congratulations on your new acquisition. Your post raises some interesting points which I'll address. I'm the very happy owner of an Intes MK66 Rumak Maksutov.
Bigzmey wrote: Wed Nov 10, 2021 2:11 am
....

As you may know most of mass produced Maks on the market are of the Gregory design, where aluminized spot on the inner face of the corrector plate serves as the secondary mirror. 150mm iOptron is of the Rumak design, where a separate secondary mirror is mounted on the inner surface of the corrector plate. This provides extra degree of freedom in configuring Mak optics. You can see the secondary glued on inside, but interestingly the corrector also has aluminized spot. Could be that they are utilizing Gregory Mak corrector blanks?
That is doubtful, the corrector blank is unsiivered. When producing a Gregory Mak corrector the blank is ground first and the silvering is done after completion. The radii of curvature of the two sides of the corrector are slightly different and optimized for the f ratio of the design. Rumaks are faster than Gregorys at f12 or even faster. Gregorys need f13 or f15 or even longer.

The silvering is odd.... For a long time I was persuaded that the iOptron was not a Rumak but a Gregory from the marketing photos. My MK66 has screws for collimation on the secondary support.
Mak-Casses in general are praised for small central obstructions. For example, 150mm Orion/Synta Gregory Mak has central obstruction of ~10% by area. iOptron 150mM Rumak is a different beast with central obstruction of ~14%, same as in 150mm/6” SCT. 6” SCT baffle opening is 27mm. I could not find any info on the baffle opening for the 150mm Synta Mak, but I would assume it to be like 6” SCT. This means that both scopes were designed for use with 1.25” EPs only. I have measured iOptron 150mm Rumak baffle opening to be at least 35mm. This is close to 8” SCT baffle tube opening.

My only explanation is that iOptron 150mm Rumak was designed to be 2” EP-friendly, compromising somewhat light gathering power and contrast. It will be fun to try 2" EPs in it, so I decided to go with Altair Astro 2” prism for the first light.
The central obstruction is better expressed in linear % rather than area % terms. The use of area is perhaps a marketing ploy to generate a smaller number. The linear central obstruction seems to be a better metric for quick assessment of contrast, etc. The MK66 has a 33% linear obstruction and so handles 2" eyepieces well.
Interestingly, most of iOptron Rumak owners report sharp and high contrast views, which makes me think that central obstruction size is just one of many optical system parameters determining contrast, and scope performance can't be solely judged just by the central obstruction size.
This is true. If you look at the MTF or point spread function it behaves interestingly for obstructed optics. Low spatial frequency contrast is depressed but high frequency contrast is enhanced compared to an unobstructed scope. See figure 104 at https://www.telescope-optics.net/obstruction.htm. It shows that obstructed scopes are better than unobstructed at very high spatial frequencies..... Better than perfect even. That comes at the loss at the low frequency end. Fracs and Newts for fuzzies, Maks and aplanatic SCTs for planets and detecting faint galaxies.
iOptron Rumak comes across as a well-built instrument. It is on the heavy side at ~14lb compared to ~12lb 150mm Synta Mak and 8.4lb 6” SCT, which says quality to me. :) While it is comfortable to handle, I feel that extra pounds place it beyond your typical grab and go mount like ES twilight I or SW AZGti, but it should ride well on SW Skytee 2 and iOptron AZ Mount Pro I have.
It is then comparable in mass to my MK66. It rarely sits on my Vixen Porta II for terrestrial use but needs the deft touch of a neurosurgeon or safecracker to balance. It's more usually on my CG5.
iOptron Rumak comes with a couple of nice features including two speed focuser and metal dew shield. I would certainly put the metal dew shield to a good use, however over the years I have mastered making my own custom dew shields from craft foam sheets and prefer them over metal ones.
The MK66 has a single speed focuser and a dew shield.
I saw a few discussions on forums about use of insulation to overcome slow acclimation of large Maks and SCTs. That sounds reasonable and I even purchased some of the reflective foam insulation but never got around to try on my SCTs. This seems to be as good occasion as any. I wanted to make the insulation easily removable because I saw reports of moisture getting under and causing some issues. I came out with two parts: wrap-around with holes for the finder shoe and mounting bar secured in place with Velcro strips, and dew shield covering the front portion of the OTA. The dew shield has matte black flocking inside.
Interestingthat you and John Barrs go this route. I've never insulated my Mak. I prefer to cold soak in advance of an observing session.
Last edited by notFritzArgelander on Wed Nov 10, 2021 5:36 am, edited 1 time in total.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
User avatar
John Donne United States of America
Orion Spur Ambassador
Articles: 0
Offline
Posts: 967
Joined: Mon Oct 05, 2020 5:34 am
3
Location: US
Status:
Offline

TSS Awards Badges

TSS Photo of the Day

Re: New to me iOptron 150mm Mak

#3

Post by John Donne »


Great report Andrey.
I like the insulation and dew shield. 👍
I look forward to your first light report.
Clear skies soon !
SCOPES :ES127 f7.5, SW100 f9 Evostar, ES80 F6, LXD75 8" f10 SCT, 2120 10" f10 SCT, ES152 f6.5.
MOUNTS: SW AZ/EQ5, MEADE LXD75, CELESTRON CG4, Farpoint Parallelogram.
BINOCULARS: CL 10X30, Pentax 8X43, 25X100 Oberwerks.
EP: Many.

"I am more than a sum of molecules.
I am more than a sum of memories or events.
I do not one day suddenly cease to be.
I am, before memory.
I am, before event.
I am"
User avatar
Bigzmey United States of America
Moderator
Moderator
Articles: 8
Offline
Posts: 7548
Joined: Sat May 11, 2019 7:55 pm
4
Location: San Diego, CA USA
Status:
Offline

TSS Awards Badges

Re: New to me iOptron 150mm Mak

#4

Post by Bigzmey »


Thanks Mark and nFA!

I have figured out the mystery of reflective spot. If you look close it is set back relative to the corrector. It is indeed a separate secondary cemented to the corrector. They left the back of the secondary untreated so you see the reflective layer through the secondary glass and the corrector glass. Since the secondary is fixed the scope is collimated at the main mirror.

Here is a fun pair of scopes: 6" F12 Rumak and 6" F5 achro. About same size and weight, compliment each other nicely as far as strengths and weaknesses go.
Rumak-150ST.jpg
Scopes: Stellarvue: SV102ED; Celestron: 9.25" EdgeHD, 8" SCT, 150ST, Onyx 80ED; iOptron: Hankmeister 6" Mak; SW: 7" Mak; Meade: 80ST.
Mounts: SW: SkyTee2, AzGTi; iOptron: AZMP; ES: Twilight I; Bresser: EXOS2; UA: MicroStar.
Binos: APM: 100-90 APO; Canon: IS 15x50; Orion: Binoviewer, LG II 15x70, WV 10x50, Nikon: AE 16x50, 10x50, 8x40.
EPs: Pentax: XWs & XFs; TeleVue: Delites, Panoptic & Plossls; ES: 68, 62; Vixen: SLVs; Baader: BCOs, Aspherics, Mark IV.
Diagonals: Baader: BBHS mirror, Zeiss Spec T2 prism, Clicklock dielectric; TeleVue: Evebrite dielectric; AltairAstro: 2" prism.
Filters: Lumicon: DeepSky, UHC, OIII, H-beta; Baader: Moon & SkyGlow, Contrast Booster, UHC-S, 6-color set; Astronomik: UHC.

Observing: DSOs: 3106 (Completed: Messier, Herschel 1, 2, 3. In progress: H2,500: 2180, S110: 77). Doubles: 2382, Comets: 34, Asteroids: 255
User avatar
notFritzArgelander
In Memory
In Memory
Articles: 0
Offline
Posts: 14925
Joined: Fri May 10, 2019 4:13 pm
4
Location: Idaho US
Status:
Offline

TSS Awards Badges

Re: New to me iOptron 150mm Mak

#5

Post by notFritzArgelander »


Bigzmey wrote: Wed Nov 10, 2021 8:56 pm Thanks Mark and nFA!

I have figured out the mystery of reflective spot. If you look close it is set back relative to the corrector. It is indeed a separate secondary cemented to the corrector. They left the back of the secondary untreated so you see the reflective layer through the secondary glass and the corrector glass. Since the secondary is fixed the scope is collimated at the main mirror.

Here is a fun pair of scopes: 6" F12 Rumak and 6" F5 achro. About same size and weight, compliment each other nicely as far as strengths and weaknesses go.

Image
Interesting. The MK66 is (rarely, 2-3 times in 20 years) collimated at the secondary.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
User avatar
John Donne United States of America
Orion Spur Ambassador
Articles: 0
Offline
Posts: 967
Joined: Mon Oct 05, 2020 5:34 am
3
Location: US
Status:
Offline

TSS Awards Badges

TSS Photo of the Day

Re: New to me iOptron 150mm Mak

#6

Post by John Donne »


Bigzmey wrote: Wed Nov 10, 2021 8:56 pm Thanks Mark and nFA!

I have figured out the mystery of reflective spot. If you look close it is set back relative to the corrector. It is indeed a separate secondary cemented to the corrector. They left the back of the secondary untreated so you see the reflective layer through the secondary glass and the corrector glass. Since the secondary is fixed the scope is collimated at the main mirror.

Here is a fun pair of scopes: 6" F12 Rumak and 6" F5 achro. About same size and weight, compliment each other nicely as far as strengths and weaknesses go.

Image
Discovery is a lot of fun Andrey.

If it ever needs collimating maybe it will be easier to do from the rear of the telescope.
As was mentioned it probably won't need collimating very often. 😊

I am looking forward to the compare of these telescopes.
SCOPES :ES127 f7.5, SW100 f9 Evostar, ES80 F6, LXD75 8" f10 SCT, 2120 10" f10 SCT, ES152 f6.5.
MOUNTS: SW AZ/EQ5, MEADE LXD75, CELESTRON CG4, Farpoint Parallelogram.
BINOCULARS: CL 10X30, Pentax 8X43, 25X100 Oberwerks.
EP: Many.

"I am more than a sum of molecules.
I am more than a sum of memories or events.
I do not one day suddenly cease to be.
I am, before memory.
I am, before event.
I am"
User avatar
Bigzmey United States of America
Moderator
Moderator
Articles: 8
Offline
Posts: 7548
Joined: Sat May 11, 2019 7:55 pm
4
Location: San Diego, CA USA
Status:
Offline

TSS Awards Badges

Re: New to me iOptron 150mm Mak

#7

Post by Bigzmey »


John Donne wrote: Wed Nov 10, 2021 9:50 pm
Bigzmey wrote: Wed Nov 10, 2021 8:56 pm Thanks Mark and nFA!

I have figured out the mystery of reflective spot. If you look close it is set back relative to the corrector. It is indeed a separate secondary cemented to the corrector. They left the back of the secondary untreated so you see the reflective layer through the secondary glass and the corrector glass. Since the secondary is fixed the scope is collimated at the main mirror.

Here is a fun pair of scopes: 6" F12 Rumak and 6" F5 achro. About same size and weight, compliment each other nicely as far as strengths and weaknesses go.

Image
Discovery is a lot of fun Andrey.

If it ever needs colonating maybe it will be easier to do from the rear of the telescope.
As was mentioned it probably won't need colummating very often. 😊
I did a brief visual check and the rumak appears collimated. Star test will show for sure. As nFA stated Maks and SCTs hold collimation quite well. Even if it goes off typically just a slight adjustment is required.
Scopes: Stellarvue: SV102ED; Celestron: 9.25" EdgeHD, 8" SCT, 150ST, Onyx 80ED; iOptron: Hankmeister 6" Mak; SW: 7" Mak; Meade: 80ST.
Mounts: SW: SkyTee2, AzGTi; iOptron: AZMP; ES: Twilight I; Bresser: EXOS2; UA: MicroStar.
Binos: APM: 100-90 APO; Canon: IS 15x50; Orion: Binoviewer, LG II 15x70, WV 10x50, Nikon: AE 16x50, 10x50, 8x40.
EPs: Pentax: XWs & XFs; TeleVue: Delites, Panoptic & Plossls; ES: 68, 62; Vixen: SLVs; Baader: BCOs, Aspherics, Mark IV.
Diagonals: Baader: BBHS mirror, Zeiss Spec T2 prism, Clicklock dielectric; TeleVue: Evebrite dielectric; AltairAstro: 2" prism.
Filters: Lumicon: DeepSky, UHC, OIII, H-beta; Baader: Moon & SkyGlow, Contrast Booster, UHC-S, 6-color set; Astronomik: UHC.

Observing: DSOs: 3106 (Completed: Messier, Herschel 1, 2, 3. In progress: H2,500: 2180, S110: 77). Doubles: 2382, Comets: 34, Asteroids: 255
User avatar
Makuser United States of America
In Memory
In Memory
Articles: 0
Offline
Posts: 6394
Joined: Mon May 06, 2019 12:53 am
4
Location: Rockledge, FL.
Status:
Offline

TSS Awards Badges

TSS Photo of the Day

Re: New to me iOptron 150mm Mak

#8

Post by Makuser »


Hi Andrey. Congratulations on receiving the iOptron 150mm Rumak telescope from Mark which was part of Henry's legacy. And you and nFA did a nice tutorial on the differences between the Rutten and Gregory Maksutov optical design telescopes. You should really enjoy using this telescope for many years and as I have mentioned on other threads, it is a great companion to the short focal length wide field 6" f/5 refractor on observing sessions. Thanks for your equipment report Andrey and we hope to see a first light report from you soon.
Marshall
Sky-Watcher 90mm f/13.8 Maksutov-Cassegrain on motorized Multimount
Orion Astroview 120ST f/5 Refractor on EQ3 mount
Celestron Comet Catcher 140mm f/3.64 Schmidt-Newtonian on alt-az mount
Celestron Omni XLT150R f/5 Refractor on CG4 mount with dual axis drives.
Orion 180mm f/15 Maksutov-Cassegrain on CG5-GT Goto mount.
Orion XT12i 12" f/4.9 Dobsonian Intelliscope.
Kamakura 7x35 Binoculars and Celestron SkyMaster 15x70 Binoculars. ZWO ASI 120MC camera.
>)))))*>
Post Reply

Create an account or sign in to join the discussion

You need to be a member in order to post a reply

Create an account

Not a member? register to join our community
Members can start their own topics & subscribe to topics
It’s free and only takes a minute

Register

Sign in

Return to “Catadioptric telescopes”