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First ASI image. Rosette.

DaveS

By DaveS
in Imaging - Deep Sky

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DaveS

DaveS

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It won't win any prizes but this is a first run with the ASI 1600 and the 80 f/4.4 There is quite a lot of tilt to get out, but at least there is only one tilt adjustment to worry about, unlike the Trius which has its own tilter.

Anyway, 18 x 5 min subs through the 3nm Ha, using the factory max DR setting. 20 Flats, 12 Darks (All I had time for) and 50 Bias.

ZWO Test.png

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DaveS

DaveS

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The camera was the cooled version, but I think I wasn't getting the full temperature drop, it was only getting to -16C

I'm not sure where to go from here.

2 things I need to sort out, get the camera orthogonal, and get the tilt out.

Beyond that I may add [NII] and [OIII] to make a NHO palette.

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DaveS

DaveS

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Hi. Yes you need darks with this camera as there's quite a lot of amp glow. There's a long thread in the Camera section.

If you look at the stars at the edges of the image you'll see they're elongated radially on one side and tangentially on the other, meaning the image plane is tilted WRT the sensor. By fiddling the screws on the tilter I hope to get them squared on.

I may also need to check the reducer spacing.

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DaveS

DaveS

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It's this one

http://www.teleskop-express.de/shop/product_info.php/info/p7224_TS-Optics-Imaging-Star-80-mm-f-4-4---6-element-Flatfield-APO-Telescope.html

Has a built-in reducer. Unfortunately the one I have differs from the picture on the site as it has a rotator instead of the tilt adjuster. Emails to TS haven't been totally helpful but I'm making a guess at the spacing. Been here before, last year but was defeatd by a combination of clouds and shortening nights.

I think overall the spacing is right, but there is tilt making the spacing and focus differ across the frame.

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DaveS

DaveS

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On 29/12/2016 at 23:11, alcol620 said:

Nice one Dave, looking forward to getting the camera. I didn't realise you needed darks with this camera as it is supposed to have low levels of noise?

As a comparison here is an image from just the light frames, nothing else. A slight crop to take out stacking edges and a slight histogram stretch to avoid burned out highlights.

Just Lights.jpg

 

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alcol620

alcol620

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Hi Dave, great detail in the image. I think the spacing from reducer/flattener is very critical and needs to be measure accurately to match the reducer/flattener being used. So would be worth checking requirements before making adjustments to tilts etc.  I may be wrong on this, would be interested in what other more experienced imagers have to say.

Happy New Year 

Alec

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DaveS

DaveS

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Thanks Alec and Paul

I emailed TS and they linked to the components on the back of the 'scope. Together they come to 16mm. Adding this to the 68mm given on the site comes to 84mm.

The BF of the ASI 1600 is 6.5mm, added to the depth of the FW (20mm) and the optical path of a 3mm thick Astrodon filter (1mm) gives a total of 27.5mm.

Subtracting this from 84mm gives me 56.5mm for the combined distance of the rotator + spacer. I think I'm pretty well there but I'll have it off the 'scope when it stops raining (Sometime Mon morning I think) and put a micrometer on it.

Paul, this looks to be a very nice match for the 80 at 2.2 sec / px, the FOV looks good too, so I really want to crack it, and I won't be beaten by recalcitrant glass!

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Davey-T

Davey-T

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8 minutes ago, DaveS said:

Hmm..just thinking...if 3mm glass adds 1 mm to the path, shouldn't I reduce the physical path by 1mm? I think so.

Will sort it out later.

Lots of discussion on this a while ago, made my brain hurt, I think the general consensus was to subtract the 1mm.

Dave

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alcol620

alcol620

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Hi folks

In terms of allowance for the filter I had this last year from Martin at FLO when I was trying to get the distance right for a reducer on my ED80:

Martin replied

Oct 29, 1:42pm
You should add 1mm to the spacing if you have a filter really, but tolerances with the components can vary, its always good to be a little short and add delrins as you can put in and take the these out. 

The proof is always in the images and if you have a hard exact spacing and then find you need to lose a mm you cant, being a bit short and using delrins allows you some flexibilty
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DaveS

DaveS

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2 hours ago, Davey-T said:

Lots of discussion on this a while ago, made my brain hurt, I think the general consensus was to subtract the 1mm.

Dave

Makes my head hurt too :D. I think Alec's post helps though.

2 hours ago, alcol620 said:

Hi folks

In terms of allowance for the filter I had this last year from Martin at FLO when I was trying to get the distance right for a reducer on my ED80:

Martin replied

Oct 29, 1:42pm
You should add 1mm to the spacing if you have a filter really, but tolerances with the components can vary, its always good to be a little short and add delrins as you can put in and take the these out. 

The proof is always in the images and if you have a hard exact spacing and then find you need to lose a mm you cant, being a bit short and using delrins allows you some flexibilty

Thanks for posting that it gives me a good starting point. Tomorrow when I uncover the 'scope to let it dry off (Damn this horrible humidity and fog) I'll pull the camera train off the 80 and measure the actual spacing. Following Martin's advice I'll start a little short and add delrin spacers as needed. I have a set already.

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DaveS

DaveS

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Thanks Dave, I'll have another look at that tomorrow when I have the camera off the 'scope.

Question I now have from reading it is, does the BF given for the ASI include the cover glass? Further reading needed.

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wxsatuser

wxsatuser

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You must add the extra distance to the imaging train as the focus point is shifted beyond the focal plane by the filter.

Depending on the filter thickness, you will need to add approx 1/3 the filter thickness to your imaging train.

Would have thought the camera makers would have factored in the sensor glass thickness in their back focus .

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DaveS

DaveS

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I would have thought so too, but the QSI doc suggested otherwise.

Yes, rethinking it, the filter adds to the optical length. I was getting in a tangle overthinking things.

Technically, the 1/3 ratio is only true for glass of RI 1.5, eg the ubiquitous BK7. Fluorite or saphire (Two popular window materials) will have slightly different ratios.

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