Good scope for photos in Galaxy Season...?

[GuillermoBarrancos]

If only the sky had more nice widefield cloudy stuff to photograph through Feb / March / April then I wouldn't even be looking I don't think! Go on, give me a long long list of all the objects I've not realised are available...!

Things certainly seem to really be pointing at the 8" EdgeHD - looks very tasty.

Back to guiding - if using an OAG, would the QHY5-II be sensitive enough?

I don't see why not. The QHY5-II gets a lot of praise. I will be buying one myself. Just tossing atm between the QHY5-II and QHY5L-IIm.

[glappkaeft]

The problem with longer focal length is that the Canon 60D the OP owns has too small pixels (4.3 microns) for focal lengths much over 1000 mm. At 1500 mm the pixel scale will be just 0.59 arcsec/px. Unless Wiltshire has unusually good seeing (FWHM commonly around 1.5") this extra resolution will be wasting photons for no gain and getting a decent signal will be hard.

Unless a new camera with say 6 micron pixels is also in the budget I'd stay with 800-1000 mm focal length.

[glappkaeft]

I'd be looking at John's images from his 6 inch RC and wondering how much better you could get from a comparable class of scope! I'll be trying the 8 inch version at some point, in all probability, but haven't done so yet. You need to budget for good collimation tools if you don't have them, I'd say.

Before you invest in a collimation telescope I'd recommend using Richard Simons guide "Collimating Ritchey-Chrétien Optics" from AIC2011. You can find it here: http://www.aicccd.com/archive/2011_presentation_archive.html

It's the method we use for the clubs 16" RC and it just requires a CCD camera. The wierd thing with RC telescopes is that they are so well corrected it is sometimes hard to see if collimation is slightly off. The stars just get a little bit (last time 0.4") larger.

[PhotoGav]

Just when I thought I was getting somewhere... along comes a very interesting post from glappkaeft. Good advice that I will be throwing into the mix.

Guillermo - as for QHY5-II or QHY5L-II, I rather regret not getting the L colour version. The one I have (mono) does the job that I purchased it for (guiding) perfectly, but it would be nice to be able to planet capture with it in colour too. Just a thought...

[glappkaeft]

I didn't even bother trying to guide with my finder guider with the C9.25. I use an OAG with it and keep the finder guider perfectly aligned on the Tak. This way I have worked out that there is minimal changeover requirements when I swap the scopes on and off (The Lodestar guide camera being the only thing that needs swapping between the two - Imaging cam obviously) - I don't know what guide camera you are using, but you do need a sensitive one - To this end I bought a Lodestar.

One cheap and quick improvement when using an OAG is to put a 0.5x focal reducer in front of the guide camera. You get smaller stars with better SNR, a field of view that is four times larger and modern guide cameras and software have no problem guiding a mount at half the focal length of the imaging optics.

[GuillermoBarrancos]

One cheap and quick improvement when using an OAG is to put a 0.5x focal reducer in front of the guide camera. You get smaller stars with better SNR, a field of view that is four times larger and modern guide cameras and software have no problem guiding a mount at half the focal length of the imaging optics.

Interesting.

[ollypenrice]

It's true that your small pixels do present a problem - but also bring more resolution to shorter focal lengths and so bring a kind of solution as well. I didn't realize that they were SO tiny though, not being much up on DSLRs. Very difficult! Finding widefield targets might be the answer!!! Huge Virgo CLustr mosaic?

Olly

[nmoushon]

I'm in the middle of a similar upgrade that you are thinking of: wanting to image galaxies. I have a very similar setup, currently, to yours. I've been researching this for about 6months now so to spare all of time I'll tell you the short version:

I first started off  with the RC vs SCT topic as well. I came the the conclussion that for me and my budget the SCT works out the best. RC can be better corrected than the SCT but you need a very large budget to afford the RC that gives this quality. The smaller/cheaer RCs tend not to be able to achieve the same that the bigger/more expensive RCs can. Another reason is that, like Olly, I don't want to have to deal with an open tube and star spikes. More so on the open tube than star spikes though. I want as little tinkering as possible. I love tinkering but when its on my terms. I don't want to have to tinker unexpectedly. Especially on expensive equipement.

I then went to deciding what f/ratio I want. This brought up the new Meade 12" f/8 SCT vs the Celestron 11" EdgeHD F/10 SCT. The short answer, as its been stated above, is that when imaging galaxies the f/ratio does not play as big as a role as if you were imaging nebula. So the need for f/8 reduced to f/5.6 is only appealing if you are trying to get the long FL images of the detail in some nebula. My take is that my main purpose of the upgrade is to image galaxies which require long FL over a faster f/ratio. So that why I turned to the EdgeHD. You can still reduce it to f/7, which is pushing the f/ratio of imaging nebula but its duable, but you get the extra FL of f/10. Combined with your DSLRs large chip will give you a very large number of targets to chose from. I doubt you'll ever run out of targets .

The next thing I went to decide was the mount. This is actually the most important part of the upgrade but I chose to match a mount to my scope than match a scope to my mount as you are doing. I'm still on the fence for me and that between a used AP900 or a new EQ8. But since you are keeping your HEQ5 you have to chose a scope that fits. In that case I would also agree with the above posts and suggest the 8" EdgeHD with reducer as the both the max size scope and the optimal scope for you.

For the reducer you actually have several options. The most common is to buy the reducer designed for the Edge series but I find them very over priced. $600 new for a 11" and I think its like $400 for the 8"...you'll have to double check he price on the 8" though. Some say that there is no other brand of recuder that works with the Edge and some say that there are others that work just as good and the are half the price. I'm still on the fence but I'm swaying towards the other brands and saving a couple hundred dollars. I could understand spending more if you have the crazy expensive cameras and such but for us that just trying to get great personal images I think the other brands will work just fine.

I also have a QHY5-II mono and plan on using that as my guide cam hooked up to an OAG. I have no worry about it being able to guide and pick up stars. I know its note as sensitive as a Lodestar but I don't think, for me, the price difference at this point is worth the upgrade. I'm aware that I might have some trouble finding a good star on some targets but I think that will be a rare occasion.

[PhotoGav]

Nmoushon, thank you so much for taking the time to give such a full response. The 8" EdgeHD does seem to be emerging the winner so far. The spanner in the works is the point that glappkaeft makes about the small pixels in the 60D at this FL. Trouble is I'm not totally understanding why it's a problem! Something to do with too much image on too little chip?

Olly's idea of a mega mosaic of the super cluster is currently the most cost effective late winter/early spring target solution!

[PaulB]

Yep I'd also second the Edge.

I use a C9.25 on a G11 and guide, though a 9x50 finder, using a Q5 and PHD. I have not had any issues with guiding.

The Edge is a good scope and the only reason that stopped me from buying an 9.25Edge was the cost of the focal reducer.

I used Newt's for visual and imaging, but. Because I don't have an obsy, I was getting more and more fed up, wasting valuable time collimating.

With a SCT collimation is far easier to do. And providing you treat the SCT with respect. It shouldn't need doing all that often.

[PhotoGav]

Thanks for that Paul. Good to hear about the guiding too. Cheers.

The Edge piggy bank has been started... Maybe by Galaxy Season 2015?!

[nmoushon]

Nmoushon, thank you so much for taking the time to give such a full response. The 8" EdgeHD does seem to be emerging the winner so far. The spanner in the works is the point that glappkaeft makes about the small pixels in the 60D at this FL. Trouble is I'm not totally understanding why it's a problem! Something to do with too much image on too little chip?

Olly's idea of a mega mosaic of the super cluster is currently the most cost effective late winter/early spring target solution!

I'm no expert at camera selection and the knowledge of cameras but from what I've learned it really boils down to this: Small pixels goes with small FL scopes. Large pixels go with large FL scopes. Thats not the whole picture but thats what I kept in mind when picking a camera. There also FoV to consider  and image scale too. I'm still learning about this and trying to master it so maybe someone else can explain in more depth than I.

But though your 60D is not the best match it will still work. It will work better if you image with the reducer on. But also consider whether or not you will upgrade to a CCD in the future? If you think that could be a possibility then I say don't worry about the camera right now and get the hang of guiding and imaging at long focal lengths.

[PhotoGav]

Good words nmoushon, thank you. Yes, I almost bought an Atik 460EX in December, but held back. So a CCD is most definitely on my wish list for the future... Along with all too many other bits and pieces!

[ollypenrice]

The pixel size business is both important and simple. Any system images a certain number of arcseconds of sky per pixel. The more arcseconds of sky that feed light into a pixel the more signal it gets. SIgnal s good because it overwhelms noise. On the other hand if something changes within the arcseconds of sky you put onto one pixel (ie there is some detail to be had) then one pixel can't present that detail. It will just sum that bit of sky into one value.

So how many arcseconds per pixel should you go for? Well, this is speed versus resolution. I have never heard anyone claim that going below about 0.5 arcsecs per pixel is worth bothering with and this is a pretty extreme value. Many would put it at a far coarser level. At heart I'm a 'broad brush' widefield imager and can even live with 3.5 arcseconds per pixel. http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/i-m7NTpzc/0/X3/CONE%2085%20106%20HaRGB%20CROP-X3.jpg But for small-on-the-skygalaxies you need finer resolution, for sure. The OP should, I think, see the camera's small pixels and inability to bin as setting the upper limit on focal length.

As usual I'm starting to sing the CCD camera song here so I'd better shut up!!

Olly

[glappkaeft]

So how many arcseconds per pixel should you go for? Well, this is speed versus resolution. I have never heard anyone claim that going below about 0.5 arcsecs per pixel is worth bothering with and this is a pretty extreme value. Many would put it at a far coarser level. At heart I'm a 'broad brush' widefield imager and can even live with 3.5 arcseconds per pixel. http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/i-m7NTpzc/0/X3/CONE%2085%20106%20HaRGB%20CROP-X3.jpg But for small-on-the-skygalaxies you need finer resolution, for sure. The OP should, I think, see the camera's small pixels and inability to bin as setting the upper limit on focal length.

You are quite right and it is an harsh reality. Double the resolution and you need to quadruple the exposure time to match the amount of light hitting each pixel. If you know the typical seeing of your observing location (thw ite I use has an average about 2.5 arcsec FWHM and have never been lower than 1.5") there is no point at all of going below half the best resolution you want to image (the Nyquist/Shannon theorem). Resolution vs. light gathering vs exposure time is always a compromise so there is no upper limit (just consider the resolution of a 8 mm fisheye lens). Premium pro-sites located at the top of mountains at Las Palmas, Hawaii or the mountains of Chile can achieve FWHM of 0.5 arcsec or lower. In Scandinavia or the UK we are happy if we reach 2 arcsec/px so usually anything significantly lower than 1 arcsec/px is just wasting light (AKA oversampling).

 

As usual I'm starting to sing the CCD camera song here so I'd better shut up!!

It is hard not to. It's a catchy tune...

[PhotoGav]

Ok thank you, it is slowly starting to make sense... I've been looking at the 12D string FOV calculator and that gives me a resolution of 0.44"/pixel for the 8" EdgeHD with 60D. How do inches equate to arc seconds?! Alternatively, how do I work out arc seconds per pixel for a given set up?

[PhotoGav]

Have I been a right dunce there and " isn't inches at all ... It's seconds..... Doh!

[PhotoGav]

It's late.....!

That's my excuse anyway!

[GuillermoBarrancos]

MartinB is selling his QHY8 camera in the clasifieds section.

Thats a nice one for the 8inch SCT.

[PhotoGav]

If I add in the 0.7x reducer, that gives me a focal length of 1422mm, still useful for galaxies (?) and 0.63"/pixel, usefully above the recommended minimum... True?

FLO Price tag = £1365.

Money well spent?

[Chris]

I think something like the 200pds with its 1000mm FL is a realistic proposition considering the OP's mount and camera pixel resolution. Its also a very cost effective option!

[GuillermoBarrancos]

If I add in the 0.7x reducer, that gives me a focal length of 1422mm, still useful for galaxies (?) and 0.63"/pixel, usefully above the recommended minimum... True?

FLO Price tag = £1365.

Money well spent?

Its definitely a nice scope, the EdgeHD8.

Even if its not the best match for your canon, you can still practice and learn imaging at long focal length, while you save up for a CCD.

Plenty of them coming up time to time in clasifieds, like now a QHY8.

In worst case its a nice visual instrument too and you can pop in a barlow and do some planetary imaging with it, as you already got a QHY5-II cam.

[glappkaeft]

Ok thank you, it is slowly starting to make sense... I've been looking at the 12D string FOV calculator and that gives me a resolution of 0.44"/pixel for the 8" EdgeHD with 60D. How do inches equate to arc seconds?! Alternatively, how do I work out arc seconds per pixel for a given set up?

It's not in inches but:

Pixel scale (in arcsex/px) = 206*pixel size (in microns)/focal length (in mm)

[nmoushon]

If I add in the 0.7x reducer, that gives me a focal length of 1422mm, still useful for galaxies (?) and 0.63"/pixel, usefully above the recommended minimum... True?

FLO Price tag = £1365.

Money well spent?

Thats the one but like I said it would be pricey. Here is an example that I was talking about: http://optecinc.com/astronomy/catalog/19407.htm  Here's the price list for them (jump down to page 6) http://optecinc.com/astronomy/prices/astronomy_price_list.pdf

As you can see its MUCH cheaper at $265 and and bit extra reduction. Whether you can get them in Europe or not I'm not sure. But have a look and do some research and I'm sure you'll find someone in Europe that make some similar. I believe I remember reading that there is a well know optician in Italy that makes a similar reducer but cant remeber. 

[swag72]

If I add in the 0.7x reducer, that gives me a focal length of 1422mm, still useful for galaxies (?) and 0.63"/pixel, usefully above the recommended minimum... True?

FLO Price tag = £1365.

Money well spent?

As you know I am new to the longer focal length game and I can echo the image scale / resolution comments already posted. I've also read a book recently (The deep sky imaging primer) that makes the point that oversampling as you would be doing in this instance (0.63"/pixel) is not gaining anything at all. In this instance you are being limited by the atmosphere. It is better to oversample as you are at least getting a better SNR (or so the book says!).

I also did a little experiment with my SCT - I took 3x1800s 1x bin and 3x1800s 2x bin and the 2x were better. They were far easier to work with, had less noise and more detail. My 2x bin in this instance is giving me an image scale of 1.42 arcsec/pixel. I would not bother with anything less than 2x bin on the SCT based on my experimentation.

What does this mean for you? I think it means that without being able to bin your camera you are not going to maximise your images.

Just my incessant wittering's!!