please help

[keyser187]

hi all

i am currently trying to stack an image of andromeda but my final image is coming out green and the histogram looks wrong, i have done a screenshot instead of trying to explain it

i am using a nexstar 6se in alt az with a celestron 6.3 reducer and a eos 11000d unmod

thx

[Guest]

Hi,

Are you using a light pollution filter by any chance, with your Canon camera?

If you are using an AStronomik CLS clip in filter then a green tinge on an unmodded camera is normal and you can proccess it out.

The on.y way to stop the un natural colour balance is to have your camera astro modified, as this filter was designed to be used with a modded camera.

If you are not using any LP filters, then there is an issue with the DSS settings.

Hope this helps

Olly

[keyser187]

thx olly

had a play with the settings and re registed n stacked.

had a little play with the post pro in DSS aand got this. Not sure what the "glow" is tho?

this is 37 mins total exposure (90x 25s subs with 40 darks) iso 1600

[Guest]

I would lower your ISO to 800, and when you stack your images in DSS make sure at the end of the process you "embedd the settings" you do NOT want to apply them, otherwise you will lose huge amounts of detail when you transfer to photoshop or what ever you use.

The image you show here looks like it has been stretched a little too much, and could also be a touch if Vignetting, what is your set up, scope, camera are using a focal reducer and so on.

Olly

[Guest]

I notice you are using a focal reducer, so the vignetting will be from that, I am guessing your spacing between the reducer and camera sensor is too far and you are pushing the reducer too much, if it is the Celestron or antares or meade SCT focal reducer then you want a spacing of close to 105mm form camera sensor to reducer lens, bearing in mind that on your camera the sensor is 45mm inside the camera, then you need a spacer of 60mm to include the 10mm of the T ring, and no more, from the front of the camera to the reducer lens.

Olly

[keyser187]

i have the visual back inbetween the reducer and the camera so basicly i have the reducer screwed to the ota, the visual back screwed to that and the cameraa with t adaptor goes into that just like prime focus. is this the wrong way to use it?

thx

[todd8137]

On my 9.25 I used a camera back not a visual back it comes with a couple a spacer rings

Do not give up drop the ISO

Pat

[Guest]

i have the visual back inbetween the reducer and the camera so basicly i have the reducer screwed to the ota, the visual back screwed to that and the cameraa with t adaptor goes into that just like prime focus. is this the wrong way to use it?

thx

You should put the reducer straight onto the back of the scope then a spacer of around 60mm it doesn't matter what it is that gets you to that distance, but the distance is very important, 105mm from the middle of the reducer lens, to the camera sensor. So like I said before the sensor is 45mm inside the camera, so whatever you have between camera and reducer need to make up the 60mm difference, the closer to the camera you have the reducer the less of a focal reduction you will get, and the further away the more it will be reduced, but these reducers like to work at there native 6.3 so you shouldn't push them too far past that, (go beyond 105mm) or you will get bad vignetting and coma at the edge of the field.

Hope this helps

Olly

[keyser187]

Thx again olly u r a star.

I just measured the distance and it looks to be about 120mm so not sure how to lose 15mm, would I need to buy a 2" t adaptor and then use spacers As required? Not sure wot a camera back is ill give it a google now.

[Guest]

Thx again olly u r a star.

I just measured the distance and it looks to be about 120mm so not sure how to lose 15mm, would I need to buy a 2" t adaptor and then use spacers As required? Not sure wot a camera back is ill give it a google now.

What you need to look for is an adjustable T adapter, I have one and it will give me from 20 mm to 50mm spacing, fit that to your camera T ring, then I have an SCT to T thread adapter which is 15mm.

So I have 45mm in the camera, 10mm T ring, 15mm SCT to T thread adapter, and I use my adjustable adapter at 30mm that give me 100mm to the front of the reducer lens, and about 105mm to the centre of the lens.

So from the telescope it is......reducer---SCT to T thread adapter---30mm adjustable T thread spacer---10mm T ring---camera

I will look up the parts for you and send you the links, give me 24 hours

Olly

[Guest]

Ok here is the list of items you need, I am assuming that the back of your scope is an SCT thread, if the reducer goes straight on then it must be.

SCT to T thread adapter approx 15mm

http://www.scopesnskies.com/prod/astroengineering/generalaccessories/deluxesctt-mountcameraadaptor.html

This is a set of three 15mm T thread extension tubes, you will use 2 of them for 30mm, I can't find the adjustable one at the moment

http://www.scopesnskies.com/prod/T%20thread%20extension%20tube/tset.html

And then your Camera T ring (10mm) which you already have and camera.

That in total will give you 100mm from camera sensor to front of reducer lens, and 105mm to the centre of the lens assembly

The reason you measure to the centre of the lens assembly is that it is made up of a focal reducer and a field Flattener, the reducer is closest to the scope and the Flattener closest to the camera, so,you are measuring to the centre between them, after the reducer and before the Flattener.

Hope that makes sense to you

Olly

[Guest]

This looks even better and cheaper

http://www.365astronomy.com/365astronomy-variable-t2-extension-tube-for-sc-telescopes-53mm-optical-length-p-3303.html

I have had things from here and are very good, this is actually superb value, you just use the 30mm tube and the SCT adapter and away you go.

Olly

[keyser187]

once again thank you very much Olly for your help and time,i spent most of the night looking into T2 adapters too and came across similar ones to your last post and i have too used this site, its where i got the reducer from . so on your recomendation i will be ordering this 2moro especially at that price and ill be back with more images for you  lot to fix

[Guest]

Yes that is a bargain price, thec SCT to T thread adapter would be that much on its own anywhere else.

Glad I could be of help, that's what these forums are for

Regards

Olly

[keyser187]

i managed to get some more of m31 last night with the distance set at 105mm but i still seem to be getting  some vignetting?. i have read that i will get some vignetting by using a reducer so is this normal or am i still going wrong somewhere?. plus the seeing conditions wernt great,very thin cloud passing over. i used a screenshot of DSS as i didnt really want to keep the image.

thx peeps

[glappkaeft]

Most camera lenses will have at least some vignetting in the best of cases. Your lens seems to have a significant amount of vignetting and the only way to physically reduce it is stepping down the lens which we generally are hesitant to do. Vignetting can however be removed through post-processing using flat calibration images.

[keyser187]

ive never been fully sure on how to take flats, all ive been using is darks n bias until recently when i read another topic on here about not needing bias with a dslr so now im just using darks. i understand about putting a tshirt over the scope with a light illuminating evenly over it but not sure wot is ment by the same orientation etc etc and also i cant use AP mode as im not using a lens? i have read up on how to do it but it gets confussing with people having diff methods and ways of doing it on diff equipment and things not being in lamen terms.

Also im sure i read on here that u can use bias frames as darks flats? cld i just use these instead as it is much easier to take bias

[dph1nm]

The easiest way to take flats is just to set up the scope for the nights observing then point somewhere towards the zenith at twilight and snap away at a random bit of sky, making sure your exposure is short enough so you don't saturated the images. You will need biases for them, but you seem to be already doing this. You can dither around a bit if you are worried about picking up bright stars.

NigelM

[glappkaeft]

Nigel is spot on with his description. The only thing I like to add is a white t-shirt stretched across the lens. Set the lens to infinite focus, the same F-number as the image and set the exposure time manually such that you get an image that is about halfway to white.

Also im sure i read on here that u can use bias frames as darks flats? cld i just use these instead as it is much easier to take bias

Bias frames can be used instead of flats if your dark current is very small. However I always use dark flats instead of bias for flats since the exposure time is so short.

[ollypenrice]

Good advice on taking flats, which will a big help. I just use a bias master as a dark for flats myself.

When balancing colour try to align the top left of the histop peak in each colour channel by cutting back the black point (moving the left slider to the right in Levels.)

Green is often a residual pest so there's a free download called Hasta La Vista Green for photoshop. (Deep Sky Colors website.)

Here's how to use levels for basic colour balance.

Olly (Penrice.)

[keyser187]

ok, well i managed to get out again the other night and take sum more of m31 which was

180x 20s subs with 50 bias 40 darks and for the first time 40 flats(which im not sure if i done right) ISO 1600

stacked in DSS and after many hours of messing with settings etc i managed to get this. total exp 48mins

am i wrong in thinking i should be getting better quality images with the equipment im using? i have seen around 30min total exp of m31 whiich look fantastic.

[Alien 13]

Hi Keyser thats not a bad image but whats the F ratio of your scope M31 has a reasonably bright core but the rest is very faint and 20s will not be enough to capture it, I have tried it with 2 min subs at F4.7 and still cant capture the outer bits.

Alan

[keyser187]

This was with my nexstar 6 ( f10) with celestron 0.63 reducer and an eos 1100d.