A Reflection.....

[RyanJones]

It's likely that this weekend I'm going to get first light on my new f/5 refractor. Although I've only been doing AP for a short time, I feel I've achieved some reasonable images with my f/10 SCT. By no means am I planning to completely give up on the slow scope, but for now my concentration will turn to the new one.

I'd like to ask you all to post any small aperture f/10 images you have in your stock piles just as a comparison for me to see how much more can be achieved. Mainly looking for DSOs as this is what I concentrated on.

So...... Show us ya 10s :thumbsup:

[Atmos]

Does drizzle integrated F/5 images count? If so....
Eagle Nebula (https://www.astrobin.com/full/354286/0/)

It is taken with a 5.1" F/5.2 refractor but drizzled so at an image scale of a F/10.4 :P

[RyanJones]

I'm going to have to say no. Although you " technically " although cleverly for filled the f/10 brief, I can't reflect on your refracted photo lol. I am in absolute awe of that image though Atmos and I'm glad you posted it.

[RickS]

That's a shame. I have a shedload of drizzled images @ f/4.9 :lol: I have some at f/9 too, though with 300mm aperture. f/10 is pretty tough unless you have *big* pixels or you're chasing bright targets like the moon and planets.

[Atmos]

I know I was being a bit sneaky there :lol:

Once I finish working on my current project I plan on installing the corrector into my 10" which will make it a 10" F/10. Even then I'm probably not fulfilling the "small aperture" part so well :P

So instead, attached is a 4" F/36 with a Nikon D810 untracked.

[RyanJones]

Hi Rick,

This is the challenge I've been facing, I've loved the challenge and capturing objects I shouldn't be in light polluted skies and for sure I will return to the challenge along the way. I think I've captured some reasonable images but I'd like to directly compare with others.

[RickS]

I think you'll find f/5 a lot more fun, Ryan. Slow f-ratios have their place but probably not a great place to start :)

Cheers,
Rick.

[RyanJones]

I'd take your 10" f/10 Colin, maybe it's not the smallest apature but I said shows ya 10s and you'd have a pair :lol:

[Gavin1234]

Show us your your favourite one Ryan.

I’ve got a 125mm f10, well my wife does anyway. I’ll pull that out and give it a go on some dso’s.

[RyanJones]

I've got 2 that I think are reasonable. This is my most recent

[RyanJones]

And this is my Eagle attempt

[cometcatcher]

8" F10 still too big?

[RyanJones]

8" and under was what I had in mind but I didn't want to start off too picky. Give us your best 8 - 10 Kevin !

[cometcatcher]

Okay but I have only had the 8" F10 for a little while. I'll just link to Astrobin since I'm on an Android. These with a DSLR.

https://astrob.in/359222/0/ m17

https://astrob.in/359335/0/ Dumbbell

https://astrob.in/359647/0/ Trifid

https://astrob.in/360309/B/ Omega Centauri

https://astrob.in/360607/0/ Centaurus A

https://astrob.in/361542/B/ M8

https://astrob.in/369439/0/ M16 new camera Zwo Asi183mm pro cooled

https://astrob.in/371878/0/ Grus triplet (latest One)

[RyanJones]

Some really nice images there Kevin. No doubt aperture makes a difference but hat I'm learning from your tech cards is that I'm intergrating about 1/2 what you have.

Thank you for sharing with me :)

P.s. - can you tell me how you get defraction lines in your images ? Do you have a spider mask or something ?

[cometcatcher]

Thanks Ryan. With the M16 image I used Noel Carboni's astronomy tools actions for photoshop. It's a plugin that has a few processing routines. Star spikes is one of them. I don't use that routine often but I did with that image.

F10 is slow going, hence the need for long total integration times. I think for most objects 10+ hours at least. I've discovered 2000mm (8") F10 shows more structure in objects than my 1000mm (10") F4 Newtonian. I originally got the 8" F10 SCT for planets but find myself preferring it for bright DSO's.

[RyanJones]

F/10 was a small step up for me after starting with an f/13 4". I'm looking forward to seeing what my new f/5 will bring but I think the challenges that I set myself up with have actually inpired me more and I've really enjoyed the challenge of capturing objects that I can barely even see the stars around visually.

[Atmos]

With a cheaper F/5 refractor colour correction is not going to be great. This means that you’ll have a lot of chromatic issues (purple halos around stars) but it also robs contrast out of what you’re imaging.
This isn’t to say that you cannot have a lot of fun with it and it can be a great learning experience but it certainly has its limitations.

[RyanJones]

I'm not expecting miracles from the f/5 but it will be something different to give a go. Another IIS member has offered me his short newt too when I'm ready so I'll have another option. Everything at the budget end of the market is going to have its limitations but I'm ok with that for now while I'm still learning the ropes.

[cometcatcher]

I used to experiment with a 120mm F5 achro refractor for imaging. If the stars are not too bright in the field you can get away with it. But something like the Orion nebula with bright field stars was horrendous. With OSC anyway. A mono cam and RGB filters help a bit if you refocus between filters, but I noticed the blue channel was still bloated. Maybe with a Semi-Apo filter it would have been better. In narrow band they work fine.

[RyanJones]

Without sounding like a complete novice, can you explain what narrow band is and what's involved in it ?

[cometcatcher]

Narrow band imaging uses very sharp bandpass filters to isolate various nebula emissions like Ha, SII and OIII. They are similar to nebula filters but isolate one passband at a time.

[ChrisV]

Can't help you Ryan. F5.9 is the highest I've ever been. And that's pushing my patience.

When I had an SCT I was always working at F3.3 with a reducer and a small sensor (224mc) for live imaging.

[RyanJones]

I see. Surely that is no good with an unmodified DSLR then ? Dedicated camera and filter wheel is the way to go for that ?

I am assuming then that you stack the various bands together ? Do you have to take as many subs for each band or is your total integration split between the various filters ?

[xelasnave]

I was reading something in startools where it effectively creates new stars and you substitute them if your stars are really crook.

I was going to try using my 150 ed refractor once and combine a red and blue filter to see if that could get better stars for a substitute approach...should make them smaller at least maybe...anyways the fact is you will learn ...I did some photos a decade ago with it and no filter and apart from the violet it was rather sharp...these days you can process it out ..I think you already enjoy the chalenge of getting the best out of your gear.
I know in syartools you can mask by colour so that would help..that sort of approach.
Alex

[cometcatcher]

No doesn't work very well with a standard DSLR. Really needs a mono camera.

The various bands are applied to an RGB colour palette. There is a lot of flexibility and creativity here as to where you put what. A common one is to put sulfur in the red channel, hydrogen in the green channel and oxygen in the blue channel, but other combinations are possible.

I don't have narrow band filters yet for my mono as they are kinda expensive. Maybe next year.

You was also asking about the F5 Achro. Here's a muck about pic I took the other night of galaxy NGC1398 with a Skywatcher 120mm F5 achro. Nothing serious it's just 3.5 minutes per channel (RGB) and luminance. I didn't even bother to take dark frames. There was some blue fringing around the bright stars but I photoshopped most of it out. Looks like my flattener spacing need attention too.

[RyanJones]

Hi Alex,

Karlzberg has been on at me about getting Startools. I downloaded the trial last night then my computer crashed so I haven't been back to it. There's a limit to how much I'm willing to process an image. I'm happy with playing around with the data, balancing, stretching, sharpening etc but I draw the line at taking out bits I don't like and replacing them. All credit to those that create great images by using this technique, I'm just saying it's not a direction I want to go.

[RyanJones]

Thank you Kevin,

The information you're providing is awesome. Thank you for taking the time. I won't keep nagging you but I do have one last question with somethings you've just written. RGB I get..... I think...... I assume that's just individual subs for each channel but what is a luminance sub ?

[Atmos]

RGB is what your DSLR takes as it has red, green and blue filters over the top of the sensor inside your camera.
It can also be individual red, green and blue filters that would be in a filter wheel.

A luminance filter is pretty much clear and allows the RGB light through but blocks the UV and IR. So luminance is used to pick up detail or to quickly detect fainter galaxies.

[xelasnave]

Colin I think you can take B/W with a dslr ...could it be used as a sort of luminance?
I dont think anything changes from something I have read but I ask nevertheless.
Alex

[Atmos]

Your DSLR takes black and white photos which is why they need to be debayered. Debayering means that it turns the RAW black and white image into a colour image.

A luminance collects all three bands in every pixel where as the DSLR has 1/4 red, 1/4 blue and 1/2 green.

[cometcatcher]

Yep, as Colin mentioned I use a filter wheel with my mono camera and shoot through separate red, green and blue filters. It's more work than one shot colour, but lets one be more creative too. Ha can be added to RGB for extra pop in nebula in other galaxies for instance.

[Karlzburg]

Would turning the dslr mono and using rgb filter produce something similar?

[Atmos]

Yep. If you were to remove the bayer matrix you would have a genuine mono camera.
Glen did this with one of his a year or two ago and built a cooling unit. He had good success with it.

It may be more expensive but it would probably be better just getting a mono sensor from ZWO or QHY. I think I remember Glen having some issues getting it all done but it was a while back now.

[RyanJones]

Who would have thought from asking people to post their favourite f/10 photos I would learn so much. Thank you all for your invaluable input. It's greatly appreciated that you've all taken the time.

The f/5 is currently having a run outside. Wow it captures so much more light..... Including moon glow :( so much more sensitive to all forms of light. It will be interesting to see how it goes with just light pollution in a couple of weeks time. I'm happy if it's reasonable and I only have to drop one stop on the ISO but if I've got to drop a couple, it kind of defeats the purpose of having a faster scope..... Thoughts ?

[Karlzburg]

Maybe a filter to drop the light pollution Ryan?

[RyanJones]

Ill see how it is without a moon and make a call then. I'm still running the subs so I can see what it turns out like

[xelasnave]

Try various iso It surprises me one can get away with 1600 but it works for me now..once its was 800 mostly ...but it will be what works with the exposure conditions permit...from seeing to mount performance...I think the faster will surprise you...try 30 seconds and work up ... higher iso may help with the colour maybe..
Just experiment.

Well tonight I set up in hope with the nikon and the 70 / 200 lens at 200 and photographed lights at a village on the distance using 6400 iso and 8 seconds...amazing.

But no stars tonight.
Alex

[doppler]

I've found this guide a good starting point for iso settings on Canon dslr's, there are also settings for Nikon and Sony cameras there as well.


http://dslr-astrophotography.com/iso-values-canon-cameras/

[RyanJones]

Thank you Rick,

I actually read that exact same site this morning. That coupled with the experience I've had with my last OTA has made me draw up a bit of a table for my settings. In my current skies, I'm never going to get the best out of my new scope. Having said that, I think I've worked out a balance. I'm going to run several diffenent exposure times tonight and record the out comes. From that site, ISO 800 seems to be the best SNR for my camera which is what I ran last night. The problem is, even at 22sec, the sky washes everything out. Tonight's recordings will be as ISO 800 and iwouldnt just run small sets at different exposure lengths to record the point at which sky glow is acceptable. Given that the moon is at nearly 90%, this will become my worst case scenario. In 1 1/2 weeks when we get back to 50% moon, I'll run the same test and record my findings. Finally in 2 1/2, I'll run the same test with a new moon. My old setup was slow enough that it would sit within the tolerances of my mount in these skies. The 22sec came from that was all I could rely on the smoothness of my mount for. 22sec at ISO 3200 created small sky glow but tolerable with a full moon so I never had the options I do now.

Along the way, I plan to carry out the same test in diffenent skies to create a long term table as reference. Needless to say, going f/5 has created some challenges for me but I'm loving the data analysis and the opportunity to create a good reference table for my subs. An opportunity I've never had.

[Cimitar]

Hi Ryan,

My imaging rig is an 8" Meade LX200 ACF.
I mainly flick between f/10 and f/7, depending on targets.
I'm really happy with the scope and like you mentioned, I love a challenge. :)

On a side note, I really enjoy getting up close and personal with my targets. Having a longer focal length is one way of achieving this. I particularly enjoyed this aspect when I captured the black hole jet in M87.
Note: all images were taken at f/10, except Trifid and NGC 253. They were shot at circa f/7 using the same equipment. Mars was captured at circa f/20 (eyepiece projection).

Cheers, Evan

[Cimitar]

In addition to what I wrote above,

After re-reading the thread I noticed you posted a Tarantula shot. This is mine I took a few years back. My processing skills were fairly ordinary at that stage so I'm keen to have another crack soon.
It's at f/7, still on the same equipment though. Just thought I'd share in case it's useful :thumbsup:

[RyanJones]

Hi Evan,

You have some incredible images there. I'm a big fan of Tarantula as an object and I'd have to say yours is simply inspirational ! The detail in the moon is also incredible.

I've really enjoyed the challenge of the f/10 and after 2 nights now with the f5, I'd have to say I'm struggling :( it just picks up too much sky glow. I know the moon is lighting up the sky like Times Square but my f/10 could deal with that within reason.

Anyway Evan, thank you very much for sharing.

[cometcatcher]

Yes, F10 does deal with sky glow somewhat better than F5. Baader make a Moon and skyglow filter that helps a little.

[RyanJones]

You know sometimes you get yourself into a rabbit hole thinking about all the different things that could be contributing to your problem and suddenly the problem seems a whole lot worst? .......

I've been thinking about the challenges I had when I first started ( not that long ago really ) and how knowing nothing meant that I could only deal with one thing at a time. The title of this thread is reflecting and I think I need to do a bit of that. Have a look at some old data and remind myself how far from that I got to with my SCT and then accept that making the f/5 sing in my skies can be done, it's just another challenge.

[cometcatcher]

Personally, I don't shoot colour in more than 50% moonlight. Doing so just makes everything harder. I've tried filters in full moonlight with OSC and they help a bit, but nothing matches a dark sky.

With narrow band imaging, it's possible to shoot Ha in full moonlight with little degradation.

[RyanJones]

Ok, so for those that are interested, here are the results of my ISO exposure test on the f/5.

I ran the ISO at 800 for all subs and took 20 of each

At 22s, 20s and 18s the sky glow was too high but interestingly the star count in DSS didn't change.

At 16s the sky glow became almost acceptable and the star count dropped by about 10%

Finally at 14s the sky glow was acceptable but the star count had now dropped by a huge 50% !

It would seem that there's a cliff that the image drops off at a certain point.

Interesting.....

Am I right in saying that an f/5 gathers light 4x as fast as the f/10 ? So in theory a 15s sub would be roughly the same as a 60s sub on the f/10 ?

[cometcatcher]

For extended objects like nebula, yes. For stars, aperture is what makes a difference.

[Cimitar]

Thanks mate :thumbsup:
I'd imagine your f/5 scope will throw up some different challenges than what you've been used to. The sky glow will certainly become an issue more quickly.


Can a single 16sec exposure show much detail in a nebula? If you use that approach will you need to take hundreds of images and stack? :question:

Have you considered guiding your f/10 scope? If your mount allows it, you could get longer exposures by guiding.

[RyanJones]

Hi Evan,

No doubt the sky glow is an issue but it always has been. You're correct that the refractor makes a monster of it quite quickly. The 16 seconds was purely part testing sequence. With the moon almost full, it's about as bad as it gets. I ran 350 subs on Helix at ISO 800 for 16 sec and I was surprised I could make it out at all. The main reason I choose Helix was the stars around it are very faint and the moon was only about 10degrees away. As I said, the absolute worst case scenario. Regarding the stacking, I'm pretty used to stacking upwards of 600 subs to only get 3 odd hours of intergation. Yes it is time consuming but it's the only way I could manage it with my mount which takes me to your last comment. Yes, I believe tracking on the mount is possible but there's very like information available. I guess it's because most people don't do what I am trying to with such a basic setup. The actual mount gets jitters as it moves around. It's driven by a plastic spur gearbox so it is never going to be smooth although I do have some modifications in mind. Time will tell if I actually do it. Regardless though, we come full circle and get back to sky glow. On the f/10 at ISO 3200, a 22sec sub ( being all the mount could reliably do cleanly ) was underexposed but I made it work so an extent. Often I would take longer shots to frame the object but anything above 40 seconds had too much sky glow anyway. With the f/5, that's theoretically only 10sec. Now iso3200 is noisey so maybe 20 sec at 1600 might work. I just have to find a new sweet spot. I'll get there, it all a part of the challenge. I must say that I'm enjoying the data collection and analysis and understanding why things work the way they do.

[Cimitar]

Hi Ryan,

I see your dilemma! Given the situation it sounds like you're doing an incredible job to make it all come together in one sense or another :)

Given that you're limited with the mount and f/10 exposure lengths, guiding probably isn't worth it at this stage. I think someone else has already mentioned narrowband imaging, which is always an option further down the track, if you can't get away to a dark site.

I currently image with an unmodified DSLR and exposures are generally 3mins at ISO 1600. I typically take 25 images and stack them together. I've never done anything with a total integration time longer than 2 hours. I know I really should drop the ISO to 800 and take more subs to get a cleaner image, however, at the moment I'm a tad impatient and just want to "see everything". After I've finished doing that I'll go back and actually dedicate the appropriate time to each target.

Cheers, Evan

[RyanJones]

Thank you Evan,

I think a lot of my efforts have been driven by a combination of a never give up attitude and also being told that what I was doing would be incredibly hard or wouldn't work...... Challenge accepted:thumbsup:

Regarding your efforts, being a tad impatient seems to be working incredibl well for you. I wouldn't change a thing lol. I can't wait till the day I'm producing stuff like yours..... I just went back and had another look at your tarantula.....

I'm sure with persistence, I'll get this new setup producing something half reasonable but it looks like it is going to consume some of my dark sky time in between moons and the poor C5 will have to take a back seat for a bit :(