Dave kay

10 hours ago, ollypenrice said:

Yes, the only issue with a Petzval design is, 'Can I get the chip onto the focal plane of the telescope with the hardware I have?' If the drawtube is too long or too short for your camera's chip distance (the distance between its front attachment point and its chip) you won't be able to. But it seems that you can, so all is good. 

However, mounting hardware can introduce tilt so the less of it you have the better - and it should all be screw fit.

As for chip tilt in the camera, there's a thread on how to tackle this. 

 

Olly

Thanks for your input Olly,

I'll have a read though the thread / watch the video and have a look at testing the tilt on my camera. 

I bought an adapter to shorten the imaging train behind the scope, hopefully this will help to.

Dave. 

1 hour ago, michael8554 said:

So you are using ZWO's recommendation for Back Spacings for two different manufacturer's OTA's with built in FF's ?

Does WO recommend 55mm Backspacing?

Does Askar recommend 55mm Backspacing ?

As I said, 

"you said the OTA's don't need a Backspacing for best star shape.

And cameras don't have Backspacing, so no need for a "55mm Backspacing".

That's only necessary if there's a 55mm backspace FF or FR involved.

Michael

Having done some more reading I'm going to buy a simple m48 to t2 adapter so I can screw the filterwheel straight onto the scope from now on. There's no need to mess about with the 55mm. 

I'm not sure that this will have any effect on the issues in my images, but it's worth a try.

Dave. 

1 hour ago, michael8554 said:

1)  It's impossible to compare the star shapes in these images because they are all 300 secs exposure, so will show differing guide errors.

Take one short exposure with each at max gain, stretch if necessary, post a jpeg, 90MB tifs aren't necessary for this analysis.

2)  "both scopes didn't require an accurate back spacing as they are both Petzval designs. "

"I used a ZWO asi294mm camera (bin1, gain 120, -10 degrees, with suggested 55mm back spacing)"

Confusion here. As you said, the OTA's don't need a Backspacing for best star shape.

And cameras don't have Backspacing, so no need for a "55mm Backspacing".

That's only necessary if there's a 55mm backspace FF or FR involved.

Just focus the camera.

Michael.

Thanks for the input Michael.

I'll take some short exposures when I get some more clear skies and I'll post the jpegs here. Should 10 secs be enough or would you go shorter? 

The two Petzval scopes I own have built in FF's in the rear of the scope. This is why I used the back spacing, suggested by ZWO, of 55mm from the back of the scope to the sensor on the 294mm. I then focussed both using a bahtinov mask, so both were bang on sharp focus. I've heard that some people don't bother with the 100% accurate back spacing whilst using scopes of this design, hence why I asked the question. 

I hope that made sense,

Dave. 

Hi Folks,

I'm looking for some advice on my images below. I took two images of the Sadr Region with my new Askar FRA400 and two with my Redcat 51. I took an initial image with each scope and then rotated the camera to get a second image. 

All four images show oval stars, but in different corners. I'm not sure what to make of the issue?

My first thoughts are tilt on the camera? 

my second thought is poor back focus? --> I'm less certain of this because I was under the impression that both scopes didn't require an accurate back spacing as they are both Petzval designs. 

Both scopes were on my EQ6-R mount and I used a ZWO asi294mm camera (bin1, gain 120, -10 degrees, with suggested 55mm back spacing) and an astronomik 6nm Ha filter. I have also attached an image of my guiding on the night. 

Any help / advice will be much appreciated as I'm a bit vexed about the whole issue. 

Thanks in advance. 

Sadr Region 300s Ha (Redcat 51) rotated with spacers.tif Sadr Region 300s Ha (Redcat 51).tif Sadr Region 300s Ha (FRA400) rotated.tif Sadr Region 300s Ha (FRA400).tif

On 27/08/2022 at 12:01, Adam J said:

Got to be honest in my practical experience most "tilt" issues turn out to be optical collimation issues. Is the pattern changing as you rotate the camera. If it's not then it's tilt. If it is then it is collimation. In a fast flat field refractor it's more likely to be collimation. However looking at the images themselves and ignoring the  pixinsight contribution completely it's the bottom left looking soft so you may well have a combination of both issues. 

Adam

Thanks for this Adam.

I'll rotate the camera on a single target when the next clear night appears. 

Fi gers crossed its just a bit of tilt or guiding errors, collimation issues would be a pain. 

Dave.  

On 27/08/2022 at 10:33, michael8554 said:

Hi Dave

Not much info on your setup and exposure duration.

I assume these are "long exposures" ?

IMO both shots display guiding errors - all the stars are elongated in the direction top left to bottom right.

I would eliminate guiding errors, then test.

Look at a single short exposure, stretched if necessary.

0.4RMS means nothing if individual RA and Dec errors are not similar.

Michael

Thanks for the input Michael.

I was guiding on an EQ6-R and the subs were 300s each. 

I'll have a look around my guiding when the next clear night arrives, hopefully it is just a guiding issue. 

Hi Folks,

I am looking for some advice. I have recently purchased an Askar FRA400 and took it out for the first time last night. I took images of two targets, the Sadr region and the Eastern Veil, and both show some odd shape stars in the corners of the image. Strangely though, the odd shaped stars are in different corners of the two images. 

I was imaging with a ZWO294MM and guiding with an ASIAIR plus at 0.4 RMS total. 

The SADR region FWHM eccentricity report from Pixinsight looks like this.

The Eastern Veil FWHM eccentricity report from Pixinsight looks like this.

Any help / advice / guidance would be much appreciated,

Thanks in advance

Dave. 

1 hour ago, rickwayne said:

Is that direction aligned with either axis? If you're not guiding, the mount shouldn't be running the DEC motor at all, so consistent drift along the DEC axis just about has to be due to polar alignment. You can use PHD on stars on the celestial equator, one on the meridian and one near the horizon, and run the Guiding Assistant tool for a few minutes to check. That will quantitate things and give you a decent estimate of your polar alignment error.

If it's aligned with the RA axis...huh. Wrong tracking rate selected (e.g. lunar)? Do your PHD guide graphs show any particular pattern?

I’m pretty sure it’s the RA blue line which just gradually wanders away from my target star. Sounds like I should take more care when setting my polar alignment. I’m going to try a few of the above ideas tomorrow and will feedback with a hopefully some success. 

Thanks for all the advice guys. I’ll try and guide straight from my computer instead. Let’s hope I have more success that way 🤞

16 minutes ago, rickwayne said:

Even if you prefer to stick with ST-4 for guiding, it's worth at least setting up a test with pulse guiding (as the others have recommended) to isolate the problem further.

What do you mean that it won't step east when you're tracking w/o your guide scope? What would ever issue a "step east" command? 

My image always seems to drift right, with or without my guidecam. Im going to give my mount a good service tonight and follow the advice above and try to guide from my computer instead. 

Hi folks,

So I’m looking for advice on guiding, as my guide system is not working properly. I have an eq3-2 mount with synscan goto. I have a guide scope attached to my zwo camera which I attach straight to the synscan auto guide port. The zwo is also attached to my computer and running with phd2.  This set up has worked fine in the past but isn’t playing ball at the moment. 
My mount doesn’t seem to step east when either guiding using phd2 or when I’m tracking without my guide scope. However, I can easily move the mount in all four directions manually using the synscan controller. I thought I might have a dodgy auto guide port connection, but buying a new cable has not solved this situation. 
If anyone could shed some light on this problem it would be greatly appreciated. 

Thanks in advance,

Dave. 
 

Hello again folks,

So I went out again on Monday night and took the following images of Vega. One with bahtinov mask and then three guided images at 30, 20 and 10 secs. What do you think about star / halo shape and possible chromatic aberrations? Thanks for any input you can offer me. 

Dave K. 

IMG_6070.CR2 IMG_6069.CR2 IMG_6067.CR2 IMG_6065.CR2

7 hours ago, Adam J said:

Well one thing is certain and thats is you have a tone of sensor tilt and so its hard to say. The sensor tilt is most likely causing your elongated stars though. In terms of the dark bands in the halo that is caused by clips in the light path or sometimes on the Esprit 80 its a notch in the lens buffer ring. Either way I would discuss with your supplier as its not normal. The sad thing is I have seen lots of this from the Esprit 80 recently.

Here take a look at this thread.

https://www.cloudynights.com/topic/691489-poor-stars-with-esprit-80ed/

Adam

Thanks for the advice Adam. Looks like the my scope has the same issue as the one in the thread. I'll be getting in touch with FLO about it to see what they recommend. 

Dave. 

43 minutes ago, Ken82 said:

This looks like lateral chromatic aberration to me. 
 

Split the RGB channels and see how they line up. you could then potentially realign to the green channel which should scale the red and blue. 
 

I think you will find red and blue are at different scales (very slightly) 

Can you post a full sub for download? 
 

ken 

57 minutes ago, Adam J said:

I am assuming that it is the chunks out of the star halo that you are concerned about?

 

Yes, thought it would be a perfect halo all round. 

1 hour ago, david_taurus83 said:

They look pretty round to me. The smaller ones look square and blocky as they are probably undersampled. Have you taken a series of images and stacked them?

Just one off images of Vega. Done some basic stacking of m31. 

Yes they are cropped. I'm using a canon 7d mark 1. 

Hi folks,

I'm looking for some advice about my SW esprit 80ed. 

I've had it for a few months and have only just started taking longer exposure pictures with my guided mount and the dedicated field flattener. 

I've uploaded two images:

1) my bahtinov mask focus with 30 sec exposure

2) 30 sec exposure of Vega without mask. 

Is there a reason why the stars are not perfectly round? Not sure if it's something I'm doing wrong or one of the lenses is out of line. 

Any help / advice would be much appreciated.