The TAIR 300mm F/4.5 for astrophotography

[Vroobel]

Hi,

I'm pleased to introduce my new small ATM project: the Russian TAIR-3-PhS 300mm F/4.5 lens adapted to the purpose of astrophotography. "Adapted" doesn't mean verified yet, I just finished working on it and will try to test it ASAP, but it works under control of INDI/Ekos.

I have it thanks to @rnobleeddy who sold me recently the set called "Zenit Photosniper". This is not a usual lens, especially focusing is... weird. It's because of the whole set: 

http://camera-wiki.org/wiki/Zenit_Photosniper

After its arrival I began thinking how to turn it into another setup. Some parts landed in the box, some others I bought and others I designed and printed. Most funny thing is that the ZWO EAF is 3.5 times more expensive than the lens... 😄

 

 

Edited January 7, 2023 by Vroobel

[happy-kat]

I like the addition of the outer tyre to the photosnipper focus control, that should help fine tuning. Good luck with first use.

[Vroobel]

Thanks.

I think so, the EAF has internal gear ratio 120:1, while my pulley has 125 teeth and the EAF pulley has 20 teeth that gives 6.25 ratio. It moves very slow, like a snail. Maybe even the snail is faster... 😂

The funny fact is that the Tair allows to focus on 3m far items, but that feature will be never used. The whole range is around 30,000 steps, so I will use maybe 1000 of them. I'm go ing to perform a proper NCFZ (New Critical Focus Zone) calculation for this set and its backlash.

Edited January 7, 2023 by Vroobel

[Ratlet]

Any chance you could upload the stl for the focus knob?  That would be handy.

I've got an almost identical setup.  Makes a great imaging scope.  If you have trouble achieving infinity focus there are 3 small screws in the silver and black bit by the objective lens, you can slacken these off and loosen the ring to get a bit more travel on the focuser.

I'm a big fan of vintage glass.  For large fov targets it's probably the most cost effective option.

[Vroobel]

Sure, I'll send PM when I'm ready. There is some explanation needed, so I have to prepare it.

[rnobleeddy]

Nice to see it in use! Looking forward to seeing the images it can produce.

[Vroobel]

I'm going to choose the California Nebula and a little bit of its surrounding as the first DSO. My 102EDT F/7 cannot capture it properly, so that's a goal in general. I don't aim in the wide field (yet?), but buying i.e. the RedCat just for some occasional play is in my case wasting money. 

[Vroobel]

Hi,

Because of the clouds and rain I performed a test of night focusing through a double glass.

 

 

ISO3200 10s :

 

ISO1600 10s :

 

ISO400 0.5s :

 

I'd like to mention that 5 single pulses of the EAF makes a visible difference, while 10 pulses means significant change. A calculated earlier (New) Critical Focus Zone gave me an initial step in the focusing process of the Ekos equal of 13 single pulses. That means the perfect focus should be found in a range of +/- 5x13 single pulses. I have to add that 1 single pulse moves the lenses 1.37 μm ! In the case of my Altair 102EDT F/7 similar 16 pulses very next to the focus point changes the HFR from 1.4 to 1.5.

The first move is to roughly find focus using the Bahtinov Mask.

[Nb888k]

Hi, 

I love your project. Please can you share the stl files? I was about to try to figure this out myself.

I use Myfocuserpro2 project for DIY focusser. And will use Nina autofocus. But I need a solution for scope rings, focusser gear etc and yours look great.

How's it been performing?

[Whistlin Bob]

Glad there was another post to highlight this project- looks great 👍

I mucked around with a Tair a couple of years ago: lots of fun, but you've taken it much further than I did. 

Not sure how your getting on, but an important learning for me was that it performed much better at f5.6 than it did wide open. Hope you're having fun with it.

Edited February 12, 2023 by Whistlin Bob
Typo

[Vroobel]

Hi,

Thanks for your reply. I didn't do too much, only the California Nebula: https://www.astrobin.com/hnlo7s/B/ . It looks quite good now, but I had a huge problem with significant red halos around all stars, which I removed manually. I used a Baader Canon ring with an extra compartment for 2" filters where my L-eXtreme was placed. Some people said that the halos could be caused by the filter. Now I declared a purchase of the full frame Optolong L-Pro filter here, on the SGL, so I'm going to give it another chance. I have only several targets for this setup: M31, M42 with the Horse Head and the Flame, maybe the America with Pelican, but it's again another filter needed.  

 

On 12/02/2023 at 00:13, Whistlin Bob said:

Not sure how your getting on, but an important learning for me was that it performed much better at f5.6 than it did wide open. Hope you're having fun with it.

 

My question is how does the F/5.6 appear better than the F/4.5?

 

[Vroobel]

On 11/02/2023 at 21:55, Nb888k said:

Hi, 

I love your project. Please can you share the stl files? I was about to try to figure this out myself.

I use Myfocuserpro2 project for DIY focusser. And will use Nina autofocus. But I need a solution for scope rings, focusser gear etc and yours look great.

How's it been performing?

I'm sorry for the late reply, after the defeat mentioned above i temporarily abandoned the project, but now it's coming back.

Are you still interested in the files?

[Ratlet]

Stopping down the lens will help with chromatic aberration.  It won't be eliminated but will be much reduced at F5.6.

If the halo's are coming from the filter though that might be a different issue.  I'm not sure on the exact cause of it, but people have gotten them on bright stars with a variety of scopes and cameras using dual band filters. 

Your image looks pretty good, but no idea how bad the halo's were to get to the final article.

Edited June 15, 2023 by Ratlet

[Vroobel]

I found one screenshot showing the raw stack. For me it's not acceptable and I won't repeat the manual halos removal anymore. 

 

[Whistlin Bob]

4 hours ago, Ratlet said:

Stopping down the lens will help with chromatic aberration.  It won't be eliminated but will be much reduced at F5.6.

This. I experienced haloes due to CA (not the filter for me as I've used the filter successfully elsewhere), plus a bit of spherical aberration which were much better at f5.6. 

 

3 hours ago, Vroobel said:

I won't repeat the manual halos removal anymore. 

Yeah- it's a painful process isn't it. There are some image editor tools that work well for this- Affinity photo has a fringe removal filter which does it in seconds .

[Vroobel]

I checked all available tools mention in the Internet, I think the fringe removal as well. Unsuccessfully. 

Thanks for the confirmation of the F/5.6, I'll try. 🙂

[Vroobel]

Hi, 

After another try, I gave up.  There is still the awful halo everywhere around stars, even with the F/5.6. I have no time for playing with that, I want a clean image to focus on the proper post-processing without continuously solving problems. I decided to move towards a decent scope of around 300mm. I was looking at several scopes from Altair, Sharpstar, WO etc. Then I realized, that to be able to capture many wide and often multiple objects with my APS-C camera I should aim lower than 300mm, so the RedCat 51 and its brothers in other colours were taken into account. Finally, I stopped my search on the Askar FMA230 which of course has 230mm fl and it's F/4.6, not F/4.9 like the RedCat. Now I have it and await a clear sky.

 

 

Edited July 24, 2023 by Vroobel

[iantaylor2uk]

Try the FRA 300

[Vroobel]

Thanks, I know that it's a great APO, but I wanted a wider field for the APS-C. The 300mm would be OK for a full-frame sensor, but if I have to buy something, then definitely prefer to use a cooled ASI2600MC than the modified Canon 6D with that.

[iantaylor2uk]

10 hours ago, Vroobel said:

Thanks, I know that it's a great APO, but I wanted a wider field for the APS-C. The 300mm would be OK for a full-frame sensor, but if I have to buy something, then definitely prefer to use a cooled ASI2600MC than the modified Canon 6D with that.

I use mine with a ZWO 071 MC Pro camera, which has an APS-C sized sensor and it gives a field of view of 4.5 degrees by 3 degrees, which is pretty wide!

[Vroobel]

I believe you. 230mm gives me wider field. I don't calculate degrees, I just use some framing tools to check, what I can image and how much. 😊

[Vroobel]

Please don't understand me wrong, I appreciate your advice. But I already purchased the FMA230 on 27th June and received it last Saturday, 22nd July. So, thanks again.  

[osbourne one-nil]

Are you still happy with your FMA230? Your Astrobin photos look great. 

I ask because I placed an order for one yesterday but then asked the store to hold on until Monday in case the ACL200 was vastly better. They seem fairly different types of lenses and the 230mm focal length of the FMA230 suits me better in framing-terms, so I think I made the right choice.

I just want a nice flat field with no hassle and I don't really crave the wider field of view the ACL200 would give me, although I could always crop if it was a lot better!

[Vroobel]

Sorry for late reply. Yes, I'm very happy with the FMA230, but I wasnt in the beginning.

I also considered the ACL200 with its 200mm fl, but the FMA230 has more versatile rings allowing me to easily install the Deep Sky Dad's EAF fastening and also guider, ASIair and dew heaters controller. Unfortunately, a declared 55mm backfocus isn't equal 55mm, but 53mm. I wanted to use an OAG which has 16.5mm optical path, but I had to return to the Evoguide and the 16.5mm reduce to 14.5mm to finally obtain pinpoint stars in corners. I'm not the only one with this problem, you can find info about it on the SGL as well. I'm very happy user of the FMA230 now. Just consider it, if you still didn't buy it.