New to me iOptron 150mm Mak
Posted: Wed Nov 10, 2021 2:11 am
Thanks to generosity of Mark (John Donne) in memory of late Henry (Hankmeister3) I am a proud owner of iOptron 150mm Maksutov-Cassegrain!
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?
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.
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 theOTA . The dew shield has matte black flocking inside.
Here is the Mak sitting alongside SV102ED on iOptron AZMP, waiting for the first light.
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?
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”
My only explanation is that iOptron 150mm Rumak was designed to be 2”
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”
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
Here is the Mak sitting alongside SV102ED on iOptron AZMP, waiting for the first light.