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I started taking interest in wide field imaging (ok, maybe not wide wide field, but wide enough for me :D ) and started with DSLR. Unmodified DSLR in red zone is not really going to bring much in terms of SNR, so I decided to switch to dedicated astro camera.

I got needed adapters (and managed to get two T2 extensions - one 5mm and other 3mm completely stuck, but that is another story) and Helios 44-4 58mm F/2 to give it a spin. I was really hoping that I could use it at F/2.

I did my math - I'll be using ASI178mmc. It has twice QE over DSLR, maybe x5 sensitivity in Ha (important for wide field nebula work), can use LPS filter, is cooled and therefore can be properly calibrated. It does have smaller pixels at 2.4um vs 3.76um but F/2 should compensate that over F/4 that I used with DSLR (both are ~55mm objective lens).

First sobering moment came when I tried to focus at F/2 - those blobs were everything but stars. I quickly learned that I need to stop the lens down to get anything usable, and yes, I needed to stop it down to at least F/4 - there goes my advantage.

I'm using AZGti in EQ mode and I was hoping to be able to get longer exposures - like 2-4 minutes. I used 30s with DSLR and that was ok with respect to polar alignment and periodic error. Second surprise was trailing at 2 minutes and excessive trailing at 4 minutes. This mount has at least something like 50-60" of P2P periodic error (about 8px worth of trail at 8.54"/px). At 60s things were fine, so I decided to go with 60s exposures.

I planed to get whole Veil complex - one hour worth of data and NGC7000 - Nan - another hour of data. Managed only first target because clouds rolled in ...

At the time of the capture I was having high hopes - eastern Veil was readily visible in single subs.

Once I did a quick calibration of the subs and quick stacking - I did not bother to debayer data I just added 2x2 groups of pixels together to get mono image without bayer matrix to see how deep I went - I was rather disappointed by result.

stack.thumb.png.c7f774b7b1ed9b99362863e30fb32baf.png

You can make out eastern and western Veil and Pickering's triangle but that is about it really. Sharpness is not there either although lens was stopped down to F/4 and effective pixel size above is 4.8um.

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22 minutes ago, vlaiv said:

I was rather disappointed by result.

Your first attempt worked out a whole lot better than mine that's for sure.

I found with my Samyang 85mm that if I wanted to use the lens wide open I had to experiment endlessly to find the correct spacing to use it with my ASI1600. I lost count of the number of times I assembled and disassembled the imaging train to find focus within the 'L' mark on the lens by introducing shims of various thickness. It was during one of those 'disassemblings' that the lens became detached from the Geoptik EoS mount and bounced around the patio! All credit to Samyang - other than a minor mark on the lens body no harm was done.

27 minutes ago, vlaiv said:

one 5mm and other 3mm completely stuck

I guess you've tried the soles of your shoes to take them apart - it always works for me.

Adrian

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5 minutes ago, Adreneline said:

I guess you've tried the soles of your shoes to take them apart - it always works for me.

I tried pretty much everything - even my own system that usually works well, but everything failed completely. I just take another T2 extension and screw it in the one being stuck. For some reason - such combination of two extensions is much easier to unscrew together (maybe load distribution or something).

In any case - 3mm is stuck to 10mm extension - I could leave them like that to get permanent 13mm combined extension, but 5mm is stuck to EOS adapter :D - I need to remove that if I'm to adopt 5.5mm rotator - something really necessary for framing.

I'm now looking at fast longer lens. 85mm or possibly 135mm to use wide open and do mosaics with small sensor. That way, even if lens is not very sharp - large effective pixel size should compensate somewhat for that (I hope).

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Well... been there.

You know, it's the king of bokeh and this applies also to astrophotography even at f/5.6. It had the most psychedelic stars I've ever seen forming circular comatic stars.

Great lens for portraits though!

IMG_20200917_183019.thumb.jpg.1bb44350bbd6171bedd91fc9c0e4ffa4.jpg

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3 minutes ago, R26 oldtimer said:

Well... been there.

You know, it's the king of bokeh and this applies also to astrophotography even at f/5.6. It had the most psychedelic stars I've ever seen forming circular comatic stars.

Did you try it in narrowband?

It just dawned on me - after successfully pulling apart those extenders ( :D yay me! ) that I could try Ha wide field imaging of milky way with my ASI1600 and 7nm Ha filter. Could be that it will give nicer stars at F/2 that way. Will test it indoors first - when I tested spacing for ASI178 indoors - it was obvious that some letters on a box were missing sharpness and contrast at F/2 vs F/4 but I had no idea how it will relate to star shapes.

Now I know what to expect - I'll be looking at really sharp small print at F/2.

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Be interesting to follow this. I've a Helios 135mm f2.8 (I think) jobby but it does have CA, but mono sounds interesting if it means no stopping down. Mine is not made in Russia.

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I've been trying to find those subs, but they are gone. Anyhow, didn't try with ha filter because of this "bokeh" effect although CA was also horrible.

The jupiter 135 f/3.5 is more decent especially with a smaller sensor and narrowband but don't expect anything better than a modern entry level 70-200 or 70-300 zoom

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1 minute ago, R26 oldtimer said:

I've been trying to find those subs, but they are gone. Anyhow, didn't try with ha filter because of this "bokeh" effect although CA was also horrible.

The jupiter 135 f/3.5 is more decent especially with a smaller sensor and narrowband but don't expect anything better than a modern entry level 70-200 or 70-300 zoom

I've got very sharp Canon 55-250 IS STM but the problem is of course - focus by wire. I can't get that to work with dedicated astro cameras on a simple Canon EF to T2 Lens adapter.

There are alternatives out there like Yongnou lens - very cheap but also not the best quality. I wonder how would one such lens compare to these vintage lenses. Then there is Samyang - but that also means rising prices (not at a premium, but still considerable amount of money).

I also have access (or rather will have access) to CZJ 50mm F/1.8 pancolar - from online reports, this should be very sharp lens, but I suspect I'll need to stop it down as well. Maybe I'll test that one as well with NB filters.

If F/4 is the best I can get with these lenses and small OSC sensor, then I would rather go with small F/6 scope (something like 60 or 70mm) and Long Perng x0.6 FF/FR giving F/3.6. That will be longer in FL but mosaic and binning can always make it shorter F/3.6 (or there about) lens - as long as it sits fine on AZGti.

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FD lens, I have several of those but only a neximage 5, but I do have an EOS to Cmount connector and all have an FD to EOS adaptor on it and one is an adaptalII to EOS.

Begs a try at the weekend. FD leans are generally cheaper as too short focal pane for modern mirrored EOS.

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1 hour ago, happy-kat said:

FD lens, I have several of those but only a neximage 5, but I do have an EOS to Cmount connector and all have an FD to EOS adaptor on it and one is an adaptalII to EOS.

Begs a try at the weekend. FD leans are generally cheaper as too short focal pane for modern mirrored EOS.

I thought that FD to EF mount contains some sort of lens that in general degrades lens performance.

EF mount has flange focal distance of 44mm while FD has flange focal distance of 42mm.

In principle we could use FD to EF mount adapter with this lens removed because we use EF mount to T2 Lens adapter that requires T2 extensions to place camera at proper distance. Only matter would be then to put camera 2mm closer than for EF lenses?

Alternative would be FD to T2 adapter?

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The adaptor with glass is needed for mirrored EOS. Mirrorless are fine as FD is 42mm so loads of space to play with. 

I've got one adapter with glass bit and one straight through.

I have old SLR AE-1 x2 bodies which the lenses were used on. Your thread reminded me of the lenses and that they are manual and I could try those with an astro camera

Edited by happy-kat

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8 minutes ago, happy-kat said:

The adaptor with glass is needed for mirrored EOS. Mirrorless are fine as FD is 42mm so loads of space to play with. 

I have old SLR AE-1 x2 bodies which the lenses were used on. Your thread reminded me of the lenses and that they are manual and I could try those with an astro camera

How would you adapt FD lens to T2 for astro camera?

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I have an EOS to cmount and it has room to fiddle with spacing.

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Just now, happy-kat said:

I have an EOS to cmount and it has room to fiddle with spacing.

Not following, how does EOS to C-mount solve FD to T2 problem? :D

 

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It's been a long day here.

This fits to the nexinage 5 and a EOS mount lens fitting. So I'm going to try it on an FD lens where I have a straight through adaptor FD to EOS.

16003755684481.jpg.fb3a352a77c060da5061bf7dca2470b6.jpg

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Well, there is this:

https://www.banggood.com/FD-EOS-Digital-Auto-Focus-Lens-Mount-Adapter-No-Glass-For-Canon-FD-to-EOS-EF-5D-7D-50D-70D-1100D-p-1048068.html?utm_source=google&utm_medium=cpc_fashion&utm_content=izzie2&utm_campaign=snew-home-ds-0327&gclid=EAIaIQobChMImvCarojx6wIVTgCiAx0AAA18EAAYASAAEgK52_D_BwE&cur_warehouse=CN

Which is good and I suppose you have one of those, but unfortunately that does not seem to fix the problem for me.

I have EOS Lens to T2 adapter - this one:

https://www.firstlightoptics.com/adapters/astro-essentials-canon-ef-lens-to-t2-adapter-for-cmosccd-cameras.html

Problem is that this adapter is 19mm of optical path and that leaves only 7.5mm with my camera.

Above FD to EOS seems to be longer than 7.5mm. FD lens - above FD to EOS clear adapter and then this EF to T2 adapter will cause FD lens not to come to focus at infinity.

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7 minutes ago, happy-kat said:

Isn't T2 that size...

Off to search

42MM but slightly different pitch

Dave

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