Jim Smith

2 hours ago, Pitch Black Skies said:

The triangular shaped stars correspond to the location of mirror clips. There should be slight gap between the clip and mirror face. It's worth popping the rear cell off for a quick look. It would only take a few minutes, just be sure to re-collimate before use.

Thanks. I'm pretty sure I screwed the clips down quite tightly when I fitted the ring baffle. They were already tight. I will loosen them and see what happens.

3 hours ago, alacant said:

The only way we've found with the Baader cc is to lose the -awful- m42 adapter and space it properly from the m48 shoulder. The best spacing is around 58mm to 59mm.

Thanks. I am using an m42 adapter but I have increased the spacing slightly with a 1mm thick, m42 ring. That seemed to help the corner stars a bit. I will look at this potential issue after I have checked the mirror clips. (Checking the mirror clips won't cost anything!)

3 hours ago, Jamgood said:

Did you give your OTA enough time to cool down outsite before shooting?

Thanks for the idea. My 130pds lives in the shed which, on a cloudy day, is no warmer than outside. So, I don't think that's the problem.

Finally, the clouds parted for a few minutes. I managed to get one 30s, ISO400 shot of the Pleiades using my usual Z50 on the 130 pds on a SW  AZ-EQ5.

But as you can see, even with the latest modifications, the triangular stars persist!

I am using a Baader MPCC mk III. I have a ring baffle fitted to the primary. I have shortened the draw tube. I have fitted a compression ring eyepiece holder. I collimated very carefully and focused with a Bahtinov mask. I think I will check out the primary clamps next!

Uncropped...

I know I'm changing too many variables at once here but in addition to shortening the focus draw tube I have replaced the standard eyepiece holder with the compression ring version and I have recollimated. I think the secondary was not as well aligned as I first thought.

Still no sign of a gap in the clouds though...:-(

2 hours ago, sagramore said:

Just a note - you can do a reversible mod by moving the primary a short way up the tube instead of sawing the focus tube. There's others in this thread with pictures of the process, but it means if you ever wanted to you can undo the change.

Too late...the deed is done! Now awaiting a clear night to see if my star shapes will improve.

Just a thought...won't you need a larger secondary if the distance between primary and secondary is shortened?

33 minutes ago, alacant said:

saw about 10mm from the end which intrudes

Thank you. A little surgery coming up!

Making progress with my 130pds. I'm using the Baader MPCC and I've fitted the mirror edge ring baffle. The focus tube protrudes about 20mm inside the main tube when I am at focus.

The two images below were from last night. SW AZ-EQ5 mount, Nikon Z50 camera, 30 second exposures. Stacked in Affinity Photo, Astroflat Pro, Topaz DeNoise AI

Can anyone suggest why I have triangular stars?

Triangulum Galaxy 81x30s...

Running Man and Orion Nebulae 72X30s...

Last night I took some more exposures with my Z50 and they were all fine. They all had the same overall hue. There was a difference though. I was using my 5" Newtonian which is much faster at f/5 than the f/12 of my Cassegrain.

I had to increase the exposure of the original batch of multicoloured images by about 3 or 4 EV in Lightroom to see much at all. I think the problem may have been caused by underexposure.

I usually use Lightroom to review my images then stack in Deep Sky Stacker or Affinity photo. I will take a look at Siril as advised.

Thanks, Jim

When I said "the raw files were the same" I meant to say "the raw files were all different colours too"!

Lightroom Classic

I took some shots of the Horsehead Nebula with my Nikon Z50 on my 8" f/12 Cassegrain. 30 seconds. ISO 1600. The white balance was set to "Direct Sunlight".

Below is a sample of some of the .tif files exported from LrC ready for stacking. As you can see, there are a variety of different colours. The raw files were the same.

What might be causing this?

Thanks, Jim

Here is my first-light shot with my new 130pds. Nothing looked badly out of place through my Cheshire collimator. The primary screws needed a small adjustment.

Nikon Z50 (aps-c), Baader MPCC. I think it's quite promising.

I think I see some elongation of corner stars... more so at the top. Also there are some strange asymmetric fans of light radiating from the central star.  From what I read, I think I need to...

1) Increase corrector to sensor spacing by a mm or two.

2) Find a way of eliminating some sensor tilt. Third locking screw?

3) Saw a lump off the end of the draw tube. (There is about 20-25mm of it inside the scope tube when in focus.)

But before I do, I thought I would post this to see if other, more experienced owners might suggest an alternative strategy.

Thanks, Jim

11 minutes ago, Stuf1978 said:

2. Star Shapes - These weren't great. I'm not sure if it's spacing or tilt.  I managed to grab 6x3 minute subs on M33 (ignore the lack of flats) to see what my stars looked like after I collimated the scope after it was delivered.  I suspect it's tilt (please correct me if I'm wrong) as the stars at the bottom of the frame were worse than at the top. I've included the image below with crops of each corner to show this. Would this compression ring help out in this case?:

I like your M33. It's a natural looking image, rather like what you might see through a biggish telescope. Did you use a coma corrector?

On 12/10/2021 at 10:52, Skyline said:

Try Es Reid. Or Scope Doctor.

Thanks, Jim

I have had a TS Optics 80mm f/6 triplet refractor for a number of years. I have recently been trying it out for astrophotography but I'm not happy with the star shapes. Some of them are distinctly triangular. I've read that this may indicate pinched optics. 

Does anyone know of a service whereby I can send my telescope off to be tested and adjusted by experts who then return it in perfect working order?

Thanks, Jim

Yes. It works. I have used Affinity Photo's white balance adjustment layer. I leave the white balance control alone and set the tint control all the way into the red. Then, I duplicate the layer and the colours now look right.

All I need now is a clear sky to try it out in anger!

Thanks again. Jim

I have now unticked it! PIPP can now read my tif files. Thank you!

RGGB matrix seems to work best. Now I just need to work out why the images have a green cast.

PIPP gives me the attached error. It was set to RAW14.

I have been experimenting with SharpCap and my Altair gpcam3 178c camera.

I captured a .tif file but I am not sure if it contains any colour information. It is attached along with the settings file.

If it does contain information how can I debayer it?

If it doesn't, then how do I capture one that does?

Thanks, Jim

Capture_00001.tif Capture_00001.CameraSettings.txt

Thanks for the report. I will look out for predicted clear skies in the early hours.

Good conditions for trying to improve my lunar imaging last night.

SW SkyMax 102 - Altair GPCAM3 178C

roi 1520x1024 - 1/125s - best 200 of 5000 in AutoStakkert - tweaked in Affinity Photo

Sigma 120-300mm f/2.8 DG OS HSM S @ 300mm and f/4.0

Nikon D5500 74x30s ISO1600

SW AZ-EQ5  Bortle 4

Affinity Photo, Astroflat Pro, Topaz Denoise

3 hours ago, alacant said:

A 105-75mm step down filter ring (or a cereal box) will give you f4.

That's an interesting idea. I might try that.

EDIT: Just ordered a 105mm to 77mm step down ring from ebay.

2 hours ago, shropshire lad said:

Ok will do ... have you done any tests for the best ISO to use, I'm never really sure what is best.

I saw a list somewhere online for best Iso for different cameras but can't find it now?

 

I've not done any formal testing but I understand that the sensor in my D5500 is "ISO invariant" so I have been using anything from ISO 200 to 1600 and increasing the exposure in post if necessary.

try this... https://dslr-astrophotography.com/iso-dslr-astrophotography/