Adreneline

5 hours ago, TossJay said:

The Poseidon has a 2mm thick window so my plan on the next clear night was to start with ~45.3mm of backspacing (44 + 2/3 +2/3) to account for the 2mm thick UV/IR and the 2mm protective window then start adding/subtracting 0.1mm spacers.  I've removed the hard stop for ease of use with my autofocuser.

Hi Mike. Sounds like a good plan - I have no experience of the Poseidon camera so cannot offer any advice. Finding the correct spacing with the SY135 is all about well informed trial and error - and patience! Hopefully a Poseidon user will pop up and offer some first hand help. Good luck.

9 minutes ago, Petrol said:

Think I'll go down the Astro Essentials Samyang Lens to M48 adapter route then shim the back focus so it's in the "L".

Just for the record I use the AstroJolo adapter which provides an M42 thread rather than M48; not sure it is still available but this is a possible alternative. The ZWO 1.25" EFW has an M42 thread either side and I prefer to have the EFW right up against the camera although I do use a shim at this interface to ensure I can achieve a 'landscape' orientation for my camera sensor.

Adrian

24 minutes ago, SAW said:

Think I might try my 600D with the Samyang & ASI Air Plus and make a note of where it focuses.

An excellent idea.

I used my 6D+SY135 in January but never got around to looking at the subs I took of M42 - they are still residing on my old ASIair Original - 20s, 40s and 60s subs - 86 of them!

I've just loaded one of the 40s subs into Siril to look at the tilt - if any - and this is the result:

The same analysis from ASTAP:

This all looks very good but close inspection of the subs might suggest the lens is very slightly too close to the sensor:

All of this does make me think I still have a tiny amount of tilt in my SY135+ASI183 image train  

I have found in the past that not all M42 extension tubes are "perfect".

Hope this is of interest.

Adrian

1 minute ago, barbulo said:

In my case, the focus point is beyond the L mark.

Is that also the case when you use the lens on a Canon dslr?

Hi Pete,

2 hours ago, Petrol said:

Am I right in thinking that the optimum back focus is achieved when the lens is focused within the "L"?

In my opinion this is essential. I used my SY135 with my Canon 6D in January this year and took a photo of the focus position after using the autofocus routine in the ASIair and checking with a BM, this was the result:

No two lens are identical, no two cameras are identical. The back focus of the cameras themselves is subject to a manufacturing tolerance so in the case of a ZWO camera you cannot be sure it is spot on 6.5mm. I fail to understand how some people state the definitive spacing is 44mm (say) for the SY135 when used with a ZWO camera. Filter thickness will have affect the spacing. I use 1mm Astronomik filters so in theory they affect the spacing by ~0.33mm.

2 hours ago, Petrol said:

If get both the back focus and tilt spot on, will the stars be round right across the image?

Haha! You would like to think so! Again, this is my opinion only, but the SY135 is a consumer dslr lens not a dedicated astrograph. If you are lucky it will be a good one. (I recently bought a dedicated astrograph lens which had been tested prior to despatch but it still didn't perform as one would expect; I am awaiting a replacement).

2 hours ago, Petrol said:

Will any vignetting will be sorted out with flats?

Well mine is! I guess it comes down to the quality of the flats.

This is my current setup - I've been through so many iterations and variations I've lost count.

I am sure there is no misalignment or droop and the NB filters I use focus in the middle of the 'L' and I still have a slightly dodgy corner. It is what it is and I am happy  

HTH

Adrian

P.S. I am also a firm believer in using a step-down-ring and not using the aperture control on the lens. I use a 49mm sdr so the lens operates at about f2.6 and you don't get facets around the stars.

1 hour ago, SAW said:

I'm still struggling to get decent stars in the corners using the Samyang 135mm and 2600MM. I've tried loads of different spacing, shims etc Have I got a bad quality lens ?

Can I ask what spacing you have between the back face of the lens and the front face of the 2600MM?

I noticed in an earlier thread (M42 et al) that you mentioned introducing an additional 0.5 mm shim/spacer. My experience of using this lens is that introducing (or removing) a 0.1 mm shim is often too much and will give rise to a significant change in (a) focus position and (b) star shapes. I have three or four ~0.1 mm shims along with ~0.2 and 0.5 so I can get step values between 0.1 and 0.5 when fine tuning. Spacing and alignment are so critical with this lens. I've owned mine for more than three years and I still can't get it perfect in one corner despite trying numerous mounting arrangements to try to ensure the alignment is perfect and the spacing is as close as I can get to within the base of the 'L'.

I am a firm believer that the focus mark should be within the base of the 'L' when focussed on a star field. I have used a Canon 6D on my lens and it focus almost dead central in the 'L' base. @Uranium235 has suggested introducing 0.01 mm shims/wedges to correct the final issues I am having but I for one don't want to go that far - it is what it is and once BlurX has worked its magic viewing at 1:1 the stars look fine to me. In my case I am convinced it is either a lens or alignment problem as the problem persists even if I swap from using my ASI183 to an ASI1600.

I now use two PrimaLuce Labs 80mm rings to support the camera (a perfect fit) and the lens (a perfect fit if I remove the padding) and if an error exists it is less than 0.1 degree (relative to a reference flat surface) - see image above in this topic thread.

You also mention using the lens at f4. I use mine at ~f2.6 achieved by using a 49 mm step-down-ring which gives much cleaner star shapes than using the in-built aperture control in the lens.

1 hour ago, SAW said:

I'm looking for something to replace the Samyang now with something that I can use the 2600MM on and still get a good wide field of view.

There are Askar alternatives at 135, 180 and 200 mm f.l.

HTH

Very nice - GCs are such a challenge!

3 minutes ago, Phillyo said:

Very nice image! I've just bought a Redcat 51 and I'm also in Lincoln so I'm looking forward to seeing what I can get with this combo

Phil

I've had my RedCat 30 months now and I love it - it's a "keeper" for me 👍

Phil

I really like the depth you have achieved in the galaxy, and all the better for the bonus SN.

Adrian

24 minutes ago, Uranium235 said:

But.... if it aint broke (and youre happy) - dont fix it!

Thanks for the detailed response Rob.

I'm not sure I want to start playing with 0.01mm shims to correct such a tiny amount of tilt - I know the devil is in the detail and it would be nice to think it was perfect but .... 

I've looked at screw tilt adjusters in the past and came to the conclusion I could spend numerous imaging sessions chasing my tiny amount of tilt and not do any imaging!

Let me/us know if ever you produce your shim design!

Thanks again.

Adrian

Just for completeness this is the rc1600 data (standalone) processed as close as I can to the SY183 and combined rc1600+SY183 data.

Adrian

Thought I would add the Samyang 135+ASI183MM component of the above image - processed as close to the original as I can get - for comparison, if anyone is interested.

Adrian

44 minutes ago, ollypenrice said:

That was worth doing!

... if for no other reason than to keep your hand in with processing  

3 minutes ago, simmo39 said:

V nice, I just dont know how you do it. I lose all will to image this time of the year!

The lack of astro-dark is a problem and the short time window just compounds the challenge. Two near identical rigs helps - when they are both singing along nicely! I've tried doing Ha and SII on the RedCat and OIII on the Samyang but the result doesn't seem as good as the method I adopted above. No Moon and Bortle 3 round here does help. I am hoping to replace the Samyang 135 with an Askar 180 + ASI183 which gives a near identical f.o.v. to the RedCat + ASI1600 - just waiting for stock to arrive.

The ups and downs and highs and lows of AP always reminds me of A Tale of Two Cities, “It was the best of times, it was the worst of times, ...... , it was the season of light, it was the season of darkness, it was the spring of hope, it was the winter of despair.” Since taking up this hobby I've now had seven winters of despair! 🤣

Despite the lack of astro-darkness it is still pretty dark in this neck of the woods so I decided to try combining data from a Samyang 135 + ASI183MM (6nm filters) with a RedCat 51 + ASI1600MM (3nm filters).

The image comprises 12 x 300s of S, H and O from both rigs amounting to 6 hours of data from one night.

Pre-processed in APP and post-processed in PI. Following cropping to remove the Samyang only region I used BlurX and NoiseX followed by StarX on a duplicate of the linear image. Each component was then subjected to careful incremental Histogram Transformation before combining with PixelMath as straight SHO. SCNR to remove the green and magenta (I don't like either!) followed by a slight saturation boost in Curves Transformation (which I am not sure it really needed). The originals were treated to a dose of EZ Soft Stretch before extracting the stars, de-stretching them in HT, and recombining with the starless image using PixelMath.

Thanks for looking.

Adrian

7 minutes ago, gorann said:

I heard Russ Croman on TAIC recently telling that a new version of BlurXT is around the corner (AI 3.0) and it is even better at fixing corner stars.

Interesting. It is not just a SY135 problem that's for sure. I know in my case it is not a sensor problem because I have used the ASI183 with a RedCat and an Askar 180 and the corner stars are consistent in all corners. All the image train is screw-tight rigid and I have even tried different spacer rings but the problem persists. DynamicCrop sorts it 😆

11 hours ago, Uranium235 said:

More of a corner test than a serious image...

I envy you your lens corner performance.

My SY135 has a dodgy corner as seen in this raw, linear, unprocessed sub - it's no big deal but nevertheless it is frustrating.

I am convinced there is no droop or misalignment of any kind in my mounting arrangement and nothing I do changes the situation.

Once BlurX has done its magic and I've cropped off the edges it does not detract from the overall image.

I still think that for a consumer camera lens it out performs many so called astrographs.

No astro-darkness and just 10 x 300s of S, H and O but it's not turned out too bad considering the lack of data.

Sadr is such a challenge to process - it's determined to steal the show.

Using the latest incarnation/variation of my SY183 setup + 6nm filters.

Will it ever stop evolving?

14 hours ago, Pete Presland said:

Nicely captured, not managed a view of Mercury this time so far.

Thank you Pete.

I was caught unawares on Monday when I saw it, and made a complete hash of trying to record the event - but so pleased that I (and the good lady) had actually managed to see it at all. When I got a second chance I thought I'd best get my act together. I've never knowingly seen Mercury (other than the transit a few years back), so I was well happy. It's been a good few months as late last year I caught a sight of Neptune and Uranus as well - both "firsts".

Adrian

4 hours ago, wimvb said:

Thanks, Adrian. I'm not sure about the exact cause. At first I suspected the focuser extension tube. But since I have more vignetting at the same side, I now suspect that it's caused by the edge of the secondary mirror. Light that hits that edge is diffracted, and that could cause such a flare. Collimation is otherwise very good, as slightly defocused stars show round, symmetrical doughnuts across most of the field. 

When astro season ends by the end of the month, I will try to get to the bottom of this, but for now, I live with it.

These things are so frustrating to track down so I wish you good luck in finding the source of the problem; whatever it does not detract from the excellent image.

Adrian

Nice image Wim and interesting write up - as always.

Looking at your image at 1:1 what is causing this to happen to the stars on the r.h.s.?

The l.h.s. of the image shows nothing similar.

Adrian

Two nights in one week and great views of Mercury setting:

This is one of 84 images I took using a Canon 6D + 50mm lens - click to open full resolution image to see Mercury between the tree and bush:

Used QuickTime to produce a video from the 84 images:

This little video (really short!) was taken with an old Canon G16 - great for low light imaging and star trails/star videos:

Adrian

I have a recollection that one of the Action suites for PhotoShop (Noel Carboni or Annie's Astro Actions) used to include an Action to add spikes.

1 hour ago, Knighty2112 said:

OK, it’s hard to judge the FOV with the video, but if Venus was higher up just out of view then looks like you got Mercury then. Well done! 

Thanks Gus. I tried using a 50mm lens but the view was mainly (upstairs, back) window frame! I then tried my Samyang 85m lens but much the same really. The 135mm was the best but as you say it is hard to judge. I was inspired to look by the AN article this month and didn't really expect to see anything to be honest. Mercury is apparently at its brightest right now but the brightness will decrease as the planet comes higher above the horizon, peaking on the 11th.

If it is clear later I shall have another go and try and pick up something that will define more precisely what I am looking at.

Thanks again.

Adrian

18 minutes ago, Knighty2112 said:

Are you sure this is Mercury? As Venus would have also been around at the time I think higher up to the left there is a good chance it is Venus instead you captured. If this was Mercury I would expect Venus to appear in shot too when Mercury is down low. Venus would have been very obvious. There are some stars that appear near the end, but Venus would have been easily the brightest thing in shot. I was observing Mercury, Venus and Mars in twilight last night and could see Mercury through my binos only, however I do have a bungalow blocking my horizon where it would have set.

Haha! Well I am certain it was not Venus as that was sitting higher in the sky (not to far away from M45) but just out of frame and was clearly the brightest object in the evening sky.

Adrian