Imaging with the Samyang 135mm f2

[ollypenrice]

On 27/12/2022 at 12:04, AstroFin said:

Very impressive first results @stevelup ! A lot of detail visible there. You have also nailed the focus and the stars are round, meaning you have accurate tracking.

I had another go at Orion, this time capturing 171x60s frames with my modified Canon 6D under Bortle 2 skies.

Full size image in my AstroBin!

Great image but one small point: round stars do not indicate accurate tracking. They are consistent with accurate tracking but so is having equivalent guiding errors on both axes, even quite significant errors.

Olly

[powerlord]

7 hours ago, ollypenrice said:

BLUR XTERMINATOR QUESTiON.

Has anyone tried BlurXT deconvolution on Samyang data? I only have a single sub so far and it doesn't produce a workable improvement, though it seems to be trying to do so. I think it might work on a stack. If you have a stack but don't have BlurXT (which needs Pixinsight as well) and would like to try it, Dropbox me the linear stack and I'll run it and send it back. PM me. The holy grail would be that it would fix corners with the lens wide open.

While we're on BlurXT, there's a PI script available here. https://www.skypixels.at/pixinsight_scripts.html  It installs in Script - Render and allows you to derive a PSF for you image and insert it manually into BlurXT instead of using the auto PSF. Some say this improves the result.

Olly

I think it should do Olly - it certainly worked with my Altair 80ED - which has rubbish stars other than the centre unflattened. and after blurX - is pretty decent.

I'll take out some SY data and see if it works with it - as I get  similar rubbish stars around sides with SY - even shot down a few stops as never worked out exact back focus yet.

[stevelup]

I've been playing some more with the data from this session. 

Changes were...

• Enabled drizzle when stacking - this seems to have reduced the noise significantly.
• Processed it as a dual narrowband image rather than RGB

 

[powerlord]

Here's some 135mm Heart and Soul I took a few weeks back with my L-ultimate and asi2600. As I say, backfocus clearly off as starts other than centre, terrrible. So as requested by @ollypenrice here's some blurX results.

starter was a linear stack, but pre cropped and background flattened in APP.

Firstly here is with a basic stretch only:

Next is BlurX with defaults (0.25 sharpen), followed by basic stretch:

And lastly, BlurX with max 0.5 sharpen, followed by basic stretch:

I'll let folk download, and zoom in and compare themselves.

 

[Elp]

Latest attempt:

 

[ollypenrice]

Would you experienced users care to comment on this, our worst corner on a 2600 chip wide open and shown here at 100%? The other corners meet the house standard. Our last tweak was a 0.2mm reduction in backfocus and was an improvement. Given that these aberrations are confined to a tight crop of one corner, we are inclined to try an image. Experience with the RASA suggests that a stack has better corners than an individual sub and Blur X might work on a stack. It didn't help the star shapes on this single sub. Seen at 50% we feel the corner looks fine and at 66% it seems acceptable.

 

 

A two-minute cosmetic fix in Ps takes the corner to here:

 

Are we in the zone?

Olly

Edited January 5, 2023 by ollypenrice
Typo

[Elp]

Considering you've addressed it a little in post it's not too bad. I find adding any sort of spacer out of the default norm top limit of 44.5mm makes me run out of focus travel (I cannot focus to infinity). So my stars elongate and that's a 13 x 9 sensor I'm using most of the time.

Edited January 5, 2023 by Elp

[ollypenrice]

19 minutes ago, Elp said:

Considering you've addressed it a little in post it's not too bad. I find adding any sort of spacer out of the default norm top limit of 44.5mm makes me run out of focus travel (I cannot focus to infinity). So my stars elongate and that's a 13 x 9 sensor I'm using most of the time.

Thanks for responding. We have an infinitely variable Baader extension in the system and, having tensioned the belt of the focus motor, we can still build a V curve at this distance, which plate solving says is slightly short of a FL of 135mm. Maybe we should stop there.

I'm curious to know how good the corner stars can be on this chip, though.

Olly

[powerlord]

I'll need to rake out some, but I though I was getting good sharp stars even with my FF 6D with mine - it was only when I added a filter (L-ultimate) in the mix that things go south - 6d or asi2600.

However, thats 1 or 2 stops in, I don't think I've ever shot fully wide open.

[Elp]

My o3 filters are the worst, makes it look like full on tilt. Ha and S2 not so much of an issue, usually I stop one down to T2.8 no matter how I'm imaging.

[Spongey]

3 hours ago, ollypenrice said:

Would you experienced users care to comment on this, our worst corner on a 2600 chip wide open and shown here at 100%? The other corners meet the house standard.

Hi Olly,

Given that the aberrations are in one corner only the likely culprit is tilt. Unfortunately with camera lenses there isn't really room for any kind of tilt adjuster but you may be able to shim in-between some spacers to achieve the same effect. Given the optical speed of the system it doesn't take much tilt or backfocus adjustment to send corner stars wonky. If you have AF capabilities I'd highly recommend trying the Hocus Focus plugin in NINA, which will perform aberration inspection throughout a focus run and report on your tilt, curvature, backfocus, etc. You can then make adjustments and re-run the AF routine to compare results and narrow in on perfection. 

For what it's worth I've never seen this lens platesolve to 135mm exactly, everyone I know who has one reports around 130-132mm. 

Cheers

[ollypenrice]

1 minute ago, Spongey said:

Hi Olly,

Given that the aberrations are in one corner only the likely culprit is tilt. Unfortunately with camera lenses there isn't really room for any kind of tilt adjuster but you may be able to shim in-between some spacers to achieve the same effect. Given the optical speed of the system it doesn't take much tilt or backfocus adjustment to send corner stars wonky. If you have AF capabilities I'd highly recommend trying the Hocus Focus plugin in NINA, which will perform aberration inspection throughout a focus run and report on your tilt, curvature, backfocus, etc. You can then make adjustments and re-run the AF routine to compare results and narrow in on perfection. 

For what it's worth I've never seen this lens platesolve to 135mm exactly, everyone I know who has one reports around 130-132mm. 

Cheers

Thanks, I think it will be tilt, as you say. I'm not sure it's worth struggling with it since disturbing this kind of setup is likely to cure one problem at the cost of provoking another. However, where would you put the shims?

Olly

[Spongey]

Just now, ollypenrice said:

Where would you put the shims?

It depends on your image train. You may be able to add some copper/tin foil layers in between the two halves of a filterwheel or adapters, for example. Bear in mind that at f/2 it will only take a few microns of tilt to throw one corner out of the corrected image plane. 

You could also try using the camera faceplate push/pull tilt adjustment screws, but these can be just as painful as the other method.

Cheers

[Elp]

Easiest place maybe just before the camera, I have lens, Eos/filter drawer adaptor, 11mm camera ring, camera. There would be sufficient area to tape a few shims onto the back body of the filter drawer to keep them in place prior to screwing the camera ring back on. At the moment I use baader aluminium rings but wouldn't want to cut them up for tilt, far cheaper buying usual engineers shim.

[ollypenrice]

2 hours ago, Spongey said:

It depends on your image train. You may be able to add some copper/tin foil layers in between the two halves of a filterwheel or adapters, for example. Bear in mind that at f/2 it will only take a few microns of tilt to throw one corner out of the corrected image plane. 

You could also try using the camera faceplate push/pull tilt adjustment screws, but these can be just as painful as the other method.

Cheers

 

1 hour ago, Elp said:

Easiest place maybe just before the camera, I have lens, Eos/filter drawer adaptor, 11mm camera ring, camera. There would be sufficient area to tape a few shims onto the back body of the filter drawer to keep them in place prior to screwing the camera ring back on. At the moment I use baader aluminium rings but wouldn't want to cut them up for tilt, far cheaper buying usual engineers shim.

Our system is all screw fit and the camera has no tilt plate. Basically the camera screws into a tube and the other end of the tube screws into the lens. The tube is telescopic, the male and female parts of it being threaded together. The camera doesn't have a face plate, just a female thread to take the telescopic adapter tube. I think we may be shim-proof! 

Personally I think we've been pretty lucky with a chip this size and a camera lens at F2. Maybe we just get on with it as is.

Olly

[Alien 13]

6 minutes ago, ollypenrice said:

 

Our system is all screw fit and the camera has no tilt plate. Basically the camera screws into a tube and the other end of the tube screws into the lens. The tube is telescopic, the male and female parts of it being threaded together. The camera doesn't have a face plate, just a female thread to take the telescopic adapter tube. I think we may be shim-proof! 

Personally I think we've been pretty lucky with a chip this size and a camera lens at F2. Maybe we just get on with it as is.

Olly

Show me a premium APO running at f/2 that could get close 😋 Regarding shims you cut up a Coke can and make one to fit under the FLO adapter that fits to the lens, the three screws with the aluminum shim might just give enough adjustment to dial out any tilt..

Alan

[Laurin Dave]

6 hours ago, ollypenrice said:

Are we in the zone?

Olly

Looks pretty good to me Olly..  if you want perfection you could try one of the Gerd Neumann Camera Tilting Units..  but really we're all just waiting to find out what one of these at f2 can do in your skies

[ollypenrice]

1 hour ago, Laurin Dave said:

Looks pretty good to me Olly..  if you want perfection you could try one of the Gerd Neumann Camera Tilting Units..  but really we're all just waiting to find out what one of these at f2 can do in your skies

Same here!

lly

[ollypenrice]

2 hours ago, Alien 13 said:

Show me a premium APO running at f/2 that could get close 😋 Regarding shims you cut up a Coke can and make one to fit under the FLO adapter that fits to the lens, the three screws with the aluminum shim might just give enough adjustment to dial out any tilt..

Alan

Thanks Alan, I'll have another look at that.   (Erm, I wouldn't drink Coca Cola if you gave me fifty quid but maybe a beer can would do instead?)

lly

Edited January 5, 2023 by ollypenrice
typo

[Alien 13]

1 minute ago, ollypenrice said:

Thanks Alan, I'll have another look at that.   (Erm, I wouldn't drink Coca Cola if you gave me fifty quid but maybe a beer can would do instead?)

lly

Nor me, it did taste OK back in the 60s when sold in glass bottles before they messed with it. A beer can will be fine the aluminum might just be compressible enough to do the job..

Alan

[aleixandrus]

Hi! I've gotten (for free) a SV106 guidescope (Svbony 60mm f4) and I'm wondering if it makes sense using it with my Samyang 135 + ASI183MM. I don't have (yet) a guidecam so I can't try... I feel it is quite a bit an overkill but, hey, its free! 😅 I'm just wondering if it makes sense try to make this "odd thing" work or if I should let it go and just get a 30mm guidescope...

Update: I'll use an EQ6-R with this setup

Edited January 9, 2023 by aleixandrus

[Elp]

If your mount can cope with the weight stick with it, it'll resolve more stars than a 30mm.

[geeklee]

2 hours ago, aleixandrus said:

I feel it is quite a bit an overkill but, hey, its free! 😅 I'm just wondering if it makes sense try to make this "odd thing" work or if I should let it go and just get a 30mm guidescope...

Yeah, just go for it!  Saves you getting something else for now and overkill is fine, it's the opposite that's usually a problem!

[powerlord]

Yup go for it. I started with 2 30mm jobs, but now use only 50mm ones (converted sw finders). Much more light ==much easier guiding.

[Gonzo]

A few pictures of my twin lens system, still a build in progress... but almost there... (waiting for the 2" filter holder to be able to add the second camera and final bracket)

If you're interested in the build https://discord.com/channels/693401540744183859/1016760448764350474