Imaging with the Samyang 135mm f2

[Tomatobro]

A 81 year old astro club member asked if I could make him a setup using some vintage  Minolta SLR lenses. Pictures attached for interest.

[desmcm]

Hi

I'm setting up a wide field system based on a samyang 135 and have read this thread with interest.

I've ordered the Astro Esstials M48 plate from FLO and I am currently trying to decide on the optical train between it and my asi2600mc pro.

One option would be to use the combined rotator/filter holder from TS:

https://www.teleskop-express.de/shop/product_info.php/info/p12074_TS-Optics-Rotation-Adapter--Filter-Holder-and-Quick-Coupling---M48-to-T2-thread.html

For those of you using it I'd very  much like help with a few  details:

- Does this screw directly onto the Astro essentials adapter plate?

- Is the total optical path length of the combined rotator/filter holder 19mm with the filter holder in place?

- For the asi2600 which has a tilt plate meaning that 17.5 of the stated 44mm back focus of the AE adapter plate is taken. This would suggest I need a 7.5mm T2 extension piece, as 44-17.5-19=7.5mm. Is this right?

Finally, I wonder a rotator is really necessary at all as it might be simpler to loosen the WO ring I will be using and rotate the lens.

In which case,  I would skip the rotator and use a zwo filter drawer (m48/m42, 21mm optical path length) I already have, and make up the remaining 5.5mm with an m48 - m48 extension tube. Does this make sense?

Thanks in advance from a relative newbie (started in this game last July),

Des

[Space Oddities]

Hello Des!

Sorry I haven't had a change to answer your PM, I'll do it here just in case it helps someone else  

- Yes the Astro Essentials adapter is a standard M48 thread, so I think it will work fine with this rotator. For the record I have the T2-T2 rotator, that I use together with a 5mm M48-T2 reducer from TS.

- It will be 19mm +/- a fraction of a mm, due to the filter itself. People usually say you need to account for an extra 1/3 of the glass thickness. They're generally 2-3mm thick, so if you add 1/3, that would make your total back focus somewhere between 19mm and ~20mm, I believe?

- Yes that's correct, although you have to account for the filter too, so you might be slightly off. Perhaps it is safer to go for a 5mm spacer, and add spacer rings (0.5-1 mm thick) to reach 44mm in total.

This being said, since it's a camera lens providing a flat field, you might not even need 44mm... Maybe it's already fine at 42mm or something. I'll let more advanced users comment on this, I'm not really sure! 

 

The rotator isn't necessary at all, indeed, but IMO the main advantage is comfort and security. You don't have to touch the lens itself, just the camera. Loosening the ring is really not the most convenient thing to do, especially when the lens is pointing close to the zenith for instance. Unlike the RedCat 51, that has some kind of 'trench'  in which the ring can rotate securely, the Samyang doesn't, and the ring just grabs the lens by the aperture ring, so to speak. Which means, it's much less secure, and you can also rotate inadvertently the aperture ring in the process... Of course this can be mitigated by adding some adhesive tape. But still, I find rotating the lens very awkward.

Also keep in mind that there's not much space left to "grab the lens". The back is covered by the ring, the middle is the focus ring, and the front might be occupied by a dew heater... Which is why I prefer a rotator on the back of the lens, I find it much easier and safer.

Since you already have the drawer, perhaps you can start without the rotator, and see if that works for you   That rotator isn't cheap, so perhaps it's wiser to try without first.

Hope that helps!

[Tomatobro]

20 hours ago, desmcm said:

I'm setting up a wide field system based on a samyang 135 and have read this thread with interest.

The only advice I can give is that I have machined up several adapters to marry the Samyang 135 to various cameras an filter wheel combos

I make the initial back focus distance about 4mm longer than the specifications suggest and mount the camera and lens in a Alt Az mount  and point it on a distant tree (about 750 metres away) and see if I can bring the branches into focus. I then disassemble, machine off 1.5mm and retest. As I get near to focus at the infinity mark I machine off another mm and again retest. Repeat the procedure till focus is obtained.I find that in general the back focus distance is about 1 to 1.5 mm shorter than the initial calculations suggest. At this I can focus at infinity and have a little bit of adjustment headroom.

This might help with the spacer question

 

[desmcm]

Thanks for the helpful replies.

I decided to follow your good advice and skip the rotator to begin with.

Managed to get everything mounted and  aligned this evening - having taken delivery of the lens from amazon around 16.00 - and big surprise, the clouds rolled in even though the forecast was for a clear night. Snapped m42 and m45 through the high clouds anyway as an act of (futile) defiance.

Can anyone recommend a Batinov mask, please? Either to buy or to print. Various designs are advertised but not sure which ones work well.

Cheers, Des

[TareqPhoto]

One day i might try to follow all the ideas about what rings people are using for their Samyang 135mm, i don't have this lens yet, but i am thinking about getting one to have a dual system of 135mm, i only have Canon EF 135mm, but many said it is not that much good as Samyang, i thing because it must be stopped down, so if i will stop it down then it means i will use it for LRGB rather than narrowbanding, because with Samyang some said they can use it even wide open, wide open which is F2 is super fast and that better match slow narrowbanding filter, with LRGB i can use even F6 for enough exposure values shorter.

 

[Space Oddities]

10 hours ago, desmcm said:

Thanks for the helpful replies.

I decided to follow your good advice and skip the rotator to begin with.

Managed to get everything mounted and  aligned this evening - having taken delivery of the lens from amazon around 16.00 - and big surprise, the clouds rolled in even though the forecast was for a clear night. Snapped m42 and m45 through the high clouds anyway as an act of (futile) defiance.

Can anyone recommend a Batinov mask, please? Either to buy or to print. Various designs are advertised but not sure which ones work well.

Cheers, Des

I'm using this one from WO. It's pricey, but it works better IMO than opaque masks, and the size is compatible with most of my scopes. So I see it as a useful investment for the future!

There are of course cheaper options, so far I was using this one: https://www.teleskop-express.de/shop/product_info.php/info/p6373_TS-Optics-Bahtinov-Maske-fuer-Astrofotografie---D--65mm-bis-100mm.html

It works fine, but being opaque, the spikes are much smaller.

[desmcm]

9 hours ago, Space Oddities said:

I'm using this one from WO. It's pricey, but it works better IMO than opaque masks, and the size is compatible with most of my scopes. So I see it as a useful investment for the future!

There are of course cheaper options, so far I was using this one: https://www.teleskop-express.de/shop/product_info.php/info/p6373_TS-Optics-Bahtinov-Maske-fuer-Astrofotografie---D--65mm-bis-100mm.html

It works fine, but being opaque, the spikes are much smaller.

Thanks for pointing this out, Pierre.

I have a WO clear Batinov mask on my z73 and they are indeed superb. Shame it is just a bit too small to fit the 135’s dew shield.

As you wrote, probably a good investment given its versatility.

best, Des

 

 

[carastro]

I bought one ages ago from Lonely Speck before I bought my Samyang 135mm, as I had problems trying to focus with other lenses.

It wasn't cheap but it is very finely cut and gives very clear spikes.  

It is this one.  I put a circular cardboard collar on the BM and it fits perfectly inside the lens collar so the mask is directly over the aperture.

https://www.lonelyspeck.com/sharpstar/

Carole 

 

[desmcm]

1 hour ago, carastro said:

I bought one ages ago from Lonely Speck before I bought my Samyang 135mm, as I had problems trying to focus with other lenses.

It wasn't cheap but it is very finely cut and gives very clear spikes.  

It is this one.  I put a circular cardboard collar on the BM and it fits perfectly inside the lens collar so the mask is directly over the aperture.

https://www.lonelyspeck.com/sharpstar/

Carole 

 

Thanks, Carole.

I've not come across this company before. Impressive looking performance.

Best, Des

[Space Oddities]

1 hour ago, desmcm said:

Thanks for pointing this out, Pierre.

I have a WO clear Batinov mask on my z73 and they are indeed superb. Shame it is just a bit too small to fit the 135’s dew shield.

As you wrote, probably a good investment given its versatility.

best, Des

 

 

Perhaps  you could actually use it with your Samyang. A very cheap way would be to buy a male-male inverter ring, 77mm (the Samyang's filter thread) to whatever the filter thread is for the dew shield. That would allow you to screw the Samyang and the dew shield together  

These adapters are mostly used to mount lenses backwards, to turn them into macro lenses. They're easy to find on Ebay or Amazon, and should be available in all sizes. That would be a nice hack!

[desmcm]

17 hours ago, Space Oddities said:

Perhaps  you could actually use it with your Samyang. A very cheap way would be to buy a male-male inverter ring, 77mm (the Samyang's filter thread) to whatever the filter thread is for the dew shield. That would allow you to screw the Samyang and the dew shield together  

These adapters are mostly used to mount lenses backwards, to turn them into macro lenses. They're easy to find on Ebay or Amazon, and should be available in all sizes. That would be a nice hack!

Hi Pierre,

 

Interesting suggestion - I'll look into it. Never knew such things existed but then again this hobby is an endless sea

of discovery (and expense) spreading out in every direction. (I watched too much Carl Sagan as a kid.)

 

Unrelated issue - is it a good/bad idea to think of putting a clear 77mm filter in front of the lens to protect it?

 

Thanks, 

Des

 

 

 

[Tomatobro]

Re the Batinov mask, the guy I purchased the fine focuser collar from also 3D printed a focus mask for me. I found that it worked but need a bright star to work well. I purchased a Williams Optics one from Flo and its a lot better. Not cheap though.

[carastro]

Quote

I've not come across this company before. Impressive looking performance.

Best, Des

I'm not sure he is a company as such, I think he is an imager who does this as a side line.   I should warn you he is based in America.  I was waiting for the customs import bill as well, but don;t know whether this one slipped through the net but I never got one.  I ordered from him because it was the only one I could find the right size at the time.  But it certainly works extremely well. 

Carole 

[Space Oddities]

On 24/02/2021 at 14:08, desmcm said:

Hi Pierre,

 

Interesting suggestion - I'll look into it. Never knew such things existed but then again this hobby is an endless sea

of discovery (and expense) spreading out in every direction. (I watched too much Carl Sagan as a kid.)

 

Unrelated issue - is it a good/bad idea to think of putting a clear 77mm filter in front of the lens to protect it?

 

Thanks, 

Des

I have found on Aliexpress a very cheap mask, that seems less coarse than standard Bahtinov masks. You might have to pay some import duties (ships from China), but for that price, it might be worth considering!

 

[desmcm]

19 minutes ago, Space Oddities said:

I have found on Aliexpress a very cheap mask, that seems less coarse than standard Bahtinov masks. You might have to pay some import duties (ships from China), but for that price, it might be worth considering!

 

Thanks, Pierre.

It would be rude not to buy it at that price. I've ordered one and will report back on how it performs - it will take a while to arrive.

 

Any thoughts on using a 77mm clear filter to protect the lens?

 

Cheers, Des

[Space Oddities]

I'm not sure... a filter can bring unwanted reflections, especially if the coatings aren't good. I wouldn't bother honestly! The front cap is pretty good, and the lens hood can also prevent dust to settle on the front element (to some extent of course).

[Adreneline]

2 hours ago, desmcm said:

Any thoughts on using a 77mm clear filter to protect the lens?

 

I use a Hoya Pro UV cut filter on my Samyang + ASI1600MM-Pro Cooled combination. I've not noticed any problems at all with reflections. One thing I have noticed however  is much better FWHM readings with my Blue and OIII filters, and to a lesser extent Green, compared with Red, SII and Ha. The filter has saved me having to use star reduction as aggresively when processing OIII masters. I would generally agree with @Space Oddities and suggest not using a filter but my experience has been positive overall.

Adrian

Edited February 25, 2021 by Adreneline
Typo

[doubledoubleswifty]

On 16/02/2021 at 18:21, Richie092 said:

Did you have to pay duty or import tax on the screen price? It looks a little too cheap to be true!

I've ordered one from Tecobuy as well.  Just got an email from them saying it's been dispatched today - I'll keep you updated how it goes!

[Paul1]

Hello everyone

I have trouble in focussing canon 80D with Samyang 135 lens, focus ring stops before star is fully focussed. I used Bahtinov mask to focus on a bright star

Are there members here with the same problem. And is there a solution

Regards 

 

[Magnum]

On 02/03/2021 at 14:37, Paul1 said:

Hello everyone

I have trouble in focussing infinity with Samyang 135 lens, focus ring stops before star is fully focussed. I used Bahtinov mask to focus on a bright star

Are there members here with the same problem. And is there a solution

Regards 

 

you can undo some locking screws under the rubber focus grip and just it to gain a little bit of back focus. but first tell us how you are3 connecting the lens to the ccd, some adapters are too thick.

Lee

[Richie092]

1 hour ago, doubledoubleswifty said:

I've ordered one from Tecobuy as well.  Just got an email from them saying it's been dispatched today - I'll keep you updated how it goes!

I bottled it and ordered from Amazon. It is sitting in front of me with the Atik EFW and 383l+ hanging off the back of it waiting for first light.

Hopefully get an hour tonight to see if I have the spacing right. M48 to M53 Adaptor 2mm -> Atik EFW2 22mm -> Atik 383L 17.5mm = (2 + 22 + 17.5) = 41.5mm (+/- 0.5mm) I may need to space it out a bit but will see.

Hopefully yours will turn up soon. What are you using it with?

[Paul1]

On 02/03/2021 at 14:51, Magnum said:

you can undo some locking screws under the rubber focus grip and just it to gain a little bit of back focus. but first tell us how you are3 connecting the lens to the ccd, some adapters are too thick.

Lee

sorry it's the canon 80D baader modified

[Space Oddities]

Have you tried focusing by day with the live view, on a very distant object? Or maybe the Moon? I would first try this before introducing a Bahtinov in the equation, to eliminate the possibility of a faulty lens.

Since you're using a DSLR, there shouldn't be a back focus issue and your lens should focus to infinity. If it doesn't, it means it's faulty, and that case I would return it to your seller. Samyang lenses are infamous for their subpar quality controls, sadly...

Also I just read that it's Baader modified. I assume the stock UV/IR filter was replaced by a Baader one, which might be thicker? And perhaps thick enough that it doesn't allow you to focus to infinity anymore? I'm not familiar with this modification, so I'm just speculating!

Edited March 2, 2021 by Space Oddities

[Paul1]

On 02/03/2021 at 16:30, Space Oddities said:

Have you tried focusing by day with the live view, on a very distant object? Or maybe the Moon? I would first try this before introducing a Bahtinov in the equation, to eliminate the possibility of a faulty lens.

Since you're using a DSLR, there shouldn't be a back focus issue and your lens should focus to infinity. If it doesn't, it means it's faulty, and that case I would return it to your seller. Samyang lenses are infamous for their subpar quality controls, sadly...

Also I just read that it's Baader modified. I assume the stock UV/IR filter was replaced by a Baader one, which might be thicker? And perhaps thick enough that it doesn't allow you to focus to infinity anymore? I'm not familiar with this modification, so I'm just speculating!

Thanks for the quick response, I'll give it a try.