Thinking of a project refractor

[Bigzmey]

I know folks use BVs with DOBs, so it is doable but will likely require an OCA to gain in-focus travel. Another consideration for DOB users is that your favorite wide field EPs would be likely too wide to work in pairs for binoviewing, so you would have to invest in pairs of slim EPs. But as Gabby says binoviewing of planets and Moon is such a relaxing and rewarding way to observe that it worth all the troubles.

[SkyHiker]

Many people use BVs with newtonians but I am not sure what OCA would be needed or if modification to the mirror position is required,
a lot of BVs come with a 1.6x

They are relaxing to use since you are using both eyes. When the planets are out I can sit and view for hours without fatigue.
I am really not sure how they would work with a astrograph though.

I hit "Enter" at Agena Astro for the William Optics 1.25" Binoviewer Package (with 1.25" Wide Angle Eyepieces and 1.6x Barlow), so now I can try it for myself. With everything included for the price I set my expectations accordingly, but the reviews look good.

[Bigzmey]

Many people use BVs with newtonians but I am not sure what OCA would be needed or if modification to the mirror position is required,
a lot of BVs come with a 1.6x

They are relaxing to use since you are using both eyes. When the planets are out I can sit and view for hours without fatigue.
I am really not sure how they would work with a astrograph though.

I hit "Enter" at Agena Astro for the William Optics 1.25" Binoviewer Package (with 1.25" Wide Angle Eyepieces and 1.6x Barlow), so now I can try it for myself. With everything included for the price I set my expectations accordingly, but the reviews look good.

Those basic prism BVs are surprisingly good. They have been rebranded under many names. I have Orion's version. After playing with them for a year I don't feel any need to upgrade to anything fancier.

[Lady Fraktor]

I am sure you will enjoy them Henk.

The big thing about considering making a dedicated BV refractor is that everything works at the native measurements.
You will find that eyepiece magnification will change more or less with the BV+ OCA and of course if you use one different than the 1.6x it will change again.
Some of the users on CN seem to get pretty frustrated figuring it all out.

On a side note, have you received you Ronchi eyepiece yet?

[SkyHiker]

The big thing about considering making a dedicated BV refractor is that everything works at the native measurements.
You will find that eyepiece magnification will change more or less with the BV+ OCA and of course if you use one different than the 1.6x it will change again.
Some of the users on CN seem to get pretty frustrated figuring it all out.

I think the 1.6x is fixed with the Barlow of the BV that I ordered, and I don't think I will change it once I have it working. I'm fine with the 20 mm eyepieces; now I usually use the 30 mm GSO superview, not too different.

On a side note, have you received you Ronchi eyepiece yet?

It has been sitting on my coffee table waiting for inspiration and good weather, too. In CA we were very lucky to have the rainfall we needed so badly but until recently it made AP nearly impossible.

I set up a few nights ago then found out that the software update to my astroberry failed (and that I was not alone in that). I rebuilt it from source code now it's working, and I just set up. It was supposed to be all clear now I see oddly shaped banded clouds. I'll try to at least do a PA and try the Ronchi next time.

[Lady Fraktor]

Check the BV when they arrive, sometimes they take a hit in shipping and a prism may shift.
This will show up as one side being noticeably dimmer than the other.

[PeterD]

a few that I have found so far, pros and cons for all.
https://www.teleskop-express.de/shop/pr ... embly.html
https://www.teleskop-express.de/shop/pr ... --OTA.html
https://www.teleskop-express.de/shop/pr ... ctive.html

The search continues!

19/04/22 Edit:
I emailed TS about my idea and #2 is out of consideration, I had forgotten the telescope has a sub-aperture corrector directly in front of the drawtube.

Indeed, both the Bresser AR-127S and also AR-152S use a sub-aperture corrector similar to Petzval design as they say. I once went for AR102S as that was the largest aperture short focal length from the range that did not use a corrector lens.

Also, I personally doubt that stating these refactors are of Fraunhofer design is perfectly correct.

Perhaps someone more experienced can correct me now. My understanding is that Fraunhofer design requires a tight spacing between crown and flint glass in range of ~10um. That is the reason why foil spacers are usually used.
However, all Bresser achromatic refractors I have ever seen do not use foil spacers. I have personally dismantled the lens cells of AR102S, AR90 and few smaller ones and they all had a plastic ring spacer >5mm wide between the crown and flint element.

One note about AR102S that may apply to the others in the same range since they use the same focuser. The focuser travel is very short. My 1.25" diagonal required much more out-focus than the focuser was able to provide. I had to buy a 50mm extension tube.

This and T2 thread on the focuser may be an advantage if one wants to fit a binoviewer I guess.

[Lady Fraktor]

Hello Peter,
I am not sure of the faster refractors but the slower Bresser I have had seemed more like a Baker than Fraunhofer.
The 102 mm f/13.2 was definitely a Baker doublet. Still a good doublet, not sure if they are easier to make.

[PeterD]

I remember me seeing that picture when i did my research in the past. I came to the same conclusion they are most likely Baker doublets. Just forgot the name. Thanks for reminding me.
I once spoke to a local distributor for Bresser and enquired if they are really Fraunhofer doublets. They did not have a slightest idea what I was talking about and just pointed me to the website where it says Fraunhofer.

[Lady Fraktor]

I did some reading during downtime at work, technically the Baker can be considered a Fraunhofer.
R2 and R3 curves are equalized and the air gap compensates for the spherical aberration caused by R2/R3.
It is still considered a contact doublet like the Fraunhofer.
When you look at the spot diagrams the Baker actually seems a bit better for controlling aberrations.

If you ever need actual information on the Bresser telescopes, call or email the shop.
I always get good accurate response from them.

[Lady Fraktor]

I have decided to purchase the Bresser 127L f/9.4 achromat for this project but the refractor will not be back in stock for a while. (july/ aug)
In the meantime I will just have to get along with using my BVs in the usual way.

One thing I have decided to do is size the tube for use of a mirror instead of prism diagonal
which will negate any cross polarization between the BV and prism.

[Lady Fraktor]

The Bresser Messier AR-127L / 1200 arrived on 14.Aug.
I did a delivery inspection and all looks well.

A couple of quick bench tests and a look around with it during the day using a 10 mm and 18 mm on high contrast targets shows a nice figure of the lens and crisp/ contrast views.
This is going to make a good platform for a dedicated BV refractor.
I will not be cutting the tube down immediately, more a winter project.

Since shortening the tube will remove the rear baffle I will be making new ones and will increase the count to 5.
Time to get the pencil and paper!