Focal reducer for C8 EdgeHD

[kwjohnson]

Hi,

This is my first post here. I'm enjoying reading all the info on video astronomy, and I am hoping to get a Lodestar C in the next few weeks. I have a C8 EdgeHD mounted on a Celestron AVX. My goal is to finish "seeing" near-live about a hundred Herschel 400 galaxies (Ursa Major, Leo, Coma, Canes, etc.) under bright surburban skies. I would like to use LodestarLive but also understand the benefits of the SX software. My question is what focal reducer I might need for this task--something readily available in the US that I don't have to wait to find used. Is the Mallincam MFR-5 a good option? Thanks for whatever advice you might have.

Kevin

[Tinker1947]

If this is the right item then it should be easily available in the USA.....Welcome to SGL....

http://www.firstlightoptics.com/reducersflatteners/celestron-reducer-lens-7x-edgehd-800.html

[shirva]

Welcome to the forum and video astronomy..ken....dragon man is the ideal guy to answer questions on mallincam products. .davy

[kwjohnson]

Thanks for the welcome. I've heard good things about the Celestron f/6.3 for the Edge scopes. Does it provide enough reduction for DSOs?

[ollypenrice]

Thanks for the welcome. I've heard good things about the Celestron f/6.3 for the Edge scopes. Does it provide enough reduction for DSOs?

The 0.63 is a reducer flattener but the Edge already has a flat field and doesn't need flattening, so this will introduce distortions. With a small fast frame camera chip this might not matter much but the 0.7 reducer-only would surely be a better bet. It seems to have come down dramatically in price (based on the link to FLO's site above) since it first appeared. SInce it will cover APS-C it looks very promising.

Olly

[nytecam]

Welcome to the Forum Kevin -  I successfully use a Meade f/3.3 FR on my 12" Meade LX200 SCT [same screw fitting as the Celestron back-plate] with the Lodestar-C camera on DSOs for 4yrs now from London - check my links.  As the 1/2" format Lodestar chip is so small [effectively giving high magnification of DSOs !] aberrations, in conjunction with your 'Edge' scope, should be minimal. 

Certainly these [and video cams] don't use APS-C sensors so that won't be an issue.  Be guided by those who use the gear and get results under LP skies   

[kwjohnson]

Olly, my mistake. I meant to refer to the newer .7 reducer. You're right that the .63 could make things a mess. That would have the advantage of working with my DSLR, which I haven't tried on my C8.

Nytecam, it looks like the Meade 3.3 is unavailable here new. Love your pictures.

[ollypenrice]

Welcome to the Forum Kevin -  I successfully use a Meade f/3.3 FR on my 12" Meade LX200 SCT [same screw fitting as the Celestron back-plate] with the Lodestar-C camera on DSOs for 4yrs now from London - check my links.  As the 1/2" format Lodestar chip is so small [effectively giving high magnification of DSOs !] aberrations, in conjunction with your 'Edge' scope, should be minimal. 

Certainly these [and video cams] don't use APS-C sensors so that won't be an issue.  Be guided by those who use the gear and get results under LP skies   

But will the 3.3 work on the OP's Edge? This has a flat field, unlike the standard SCT. Genuine question, meaning I have no idea whether it would or wouldn't.

A 3.3 would be easy to find on the used market because on the sizes of chip now common in deep sky cameras its image circle is simply too small.

A small chip effectively gives a high magnification? Isn't this like saying that looking through a straw is like looking through a telescope? 

Olly

[DoctorD]

Hi Olly

I'd do not know about using the F3.3 with the Edge, but I'm happy with the results I get with it on my Vintage C8 - not going to achieve the kind of results seen in the Astrophotography forum but keeps me happy! 

I guess it is a bit like looking down a straw and the arc seconds per pixel may not be optimal (I get about 3 arcseconds per pixel but I think I'm pushing it a little far at F2.9).

Like anything, we have to choose our targets to fit the FoV.

Clear skies

p.s. Thanks for the reducer - as you can see it's getting some use!

[nytecam]

 That would have the advantage of working with my DSLR, which I haven't tried on my C8.

Nytecam, it looks like the Meade 3.3 is unavailable here new. Love your pictures.

The Lodestar [and other similarly chipped cams] are far 'faster' than DSLRs and speed in both OTA and camera are vital in video-like imaging in the very brief exposures we use.  Olly has advised elsewhere that anything >20m exp is not AP so we're doing fine!

Re f/3.3 FR - you can buy s/h - I did !  There must be acres of astro stuff doing nothing so check classified and post a wanted ad if need be 

[Joves]

I have the MFR-5 reducer and it works great on my LX90 ACF.

[kwjohnson]

Thanks for the input everyone. I did find a post in a Yahoo group where Mallincam said the MFR-5 works with the Edge scopes. So it looks like I have some options.

[ollypenrice]

The Lodestar [and other similarly chipped cams] are far 'faster' than DSLRs and speed in both OTA and camera are vital in video-like imaging in the very brief exposures we use.  Olly has advised elsewhere that anything >20m exp is not AP so we're doing fine!

Re f/3.3 FR - you can buy s/h - I did !  There must be acres of astro stuff doing nothing so check classified and post a wanted ad if need be 

Please, this is utter nonsense and I have never said any such thing. I advocate long exposures where the sky conditions allow and it is perfectly true that I have no time for claims that 200x1 minutes equates to 20 x10 minutes at a dark site because I know for certain that that this is not so.

It is wrong to misrepresent other members of the forum. I would not invent quotations and attribute them to you, nytecam, and I would prefer you not to invent them and attribute them to me. If I'm a little sensitive in this matter it is because I am a professional provider and I do not want anybody to believe that I think deep sky imaging begins at 20 minutes. I absolutely do not believe this and have never suggested that I did.

4x1 minutes, if I remember correctly. Nothing special but I routinely use ten minute subs for RGB.

Olly

[nytecam]

Please, this is utter nonsense and I have never said any such thing. I advocate long exposures where the sky conditions allow and it is perfectly true that I have no time for claims that 200x1 minutes equates to 20 x10 minutes at a dark site because I know for certain that that this is not so.

It is wrong to misrepresent other members of the forum. I would not invent quotations and attribute them to you, nytecam, and I would prefer you not to invent them and attribute them to me. If I'm a little sensitive in this matter it is because I am a professional provider and I do not want anybody to believe that I think deep sky imaging begins at 20 minutes. I absolutely do not believe this and have never suggested that I did.

Olly

Morning Olly - thanks to the SGL Search option I found your statement you dispute...it stuck in my memory at the time and got a mention when I showed my modest 3 - 4min exposure DSO shots to my local astro soc in spring 2013 taken with my 30cm SCT+Lodestar-C OSC as a prime imager.   I'm very happy with Video/ electronic assist mode imaging and have done so for over two decades.  There are many different ways to do AP 

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http://stargazerslounge.com/topic/177213-ccd-viable-under-uk-skies/page-2?hl=olly+20#entry182785

SGL/ Cameras/ CCD viable under UK skies?  Started by earth titan, Feb 12 2013 03:58 PM

"  10x2 minutes? Well, I guess if you're going to go as short as that then literally the time taken to change the filters plays a part! To be honest I can't say much about 20 minute images because for me that isn't astrophotography. I'm most certainly not condemning anyone for whom it is, though. And, yes, it might be better to use OSC for a 20 minute image. I suppose that for a twenty minute image you wouldn't take flats at all, but it is true that OSC reduces the flats workload.

Once you start to take a more serious image, though, I don't think processing an OSC is much faster than processing an LRGB. It can be harder because, at least in my experience, OSC can be a bit fickle on some targets.

Olly "

[RobH]

Nytecam.

It is obvious that Olly is talking about an image that has a total exposure of 20 minutes, not, as you stated, exposures ( subs in other words) of 20 minutes and above.

Any image of the night sky that isn't of clouds is astro photography of course, no matter the length.

You've misrepresented what he said, and he has every right to be displeased about that, but to me it looks like a simple misunderstanding, so can we all say sorry and get back on track please.

[michael.h.f.wilkinson]

Back on topic, I gather the 0.33x (F/3.3) reducer/flatteners where only intended for SCTs, not Edge/HDs (which did not exist when the 0.33x came out). They will most likely introduce field curvature.

It is a bit pointless to talk about magnification if eyepieces are not involved, all you can talk about is image scale in arcsec per pixel. This number also dictates which number of photons hits a given pixel, for a given flux. This ultimately determines the signal-to-noise ratio (together with thermal noise). Assuming quantum efficiency and thermal noise remain the same, a 10mm chip sporting 1024x1024 pixels used at F/3.3 will obtain essentially the same image, with the same quality, as a 20mm chip also with 1024x1024 at F/6.6, because both systems have the same image scale in arcsec per pixel. Strangely, focal ratio does not come into it. Thus, in order to gather more photons per pixel in a given exposure time image scale needs to be increased and therefore resolution must be sacrificed (just like binning does). DSO imagers sacrifice resolution all the time. Common pixel sizes used in CCDs require F/15-F/30 or so to sample at the Nyquist frequency, to prevent loss of resolution. Only planetary imagers use those kind of F-ratios.

The potential problem of small CCD chips with many pixels (to preserve resolution), is that the pixels become very small, and therefore the potential wells gathering the electrons are small as well. This limits dynamic range.

Note that the image circle of the 0.33x is about 15mm (back-of-the-envelope calculation), so your chip size needs to fit within that if it is to work at all.

[shirva]

Nice write up Michael. .davy

[shirva]

Agree with your point rob an image however long is still an image..this being the video section the images taken from a video capture in near live time are still images of a video to show what you saw live ..maybe it then comes under astrophotography if said image is stacked.that being the case video is crossing to ap so are we know looking at a hybrid situation. .whats everyone's thoughts

[ollypenrice]

Actually I remember that I do have a guest who used a 6.3 with a Meade ACF. His chip was farily small, an SBIG ST10, but this would be bigger than the video chips in question here. He said he needed some cropping of edge distortions. If you could borrow one, or even borrow a 3.3, it might be worth a try at least.

Olly

By the way, I consider any image of the clear night sky to be an astrophoto. In the full version of my other comment I was saying what AP is for me (that is to say, as I do it), but I think I made it clear that for others it can be whatever they want it to be. Anyway I'm happy provided nobody thinks I'm dismissive of video astronomy. If I did more outreach work than I do then a real time sensitive video camera would be on my list.

[kwjohnson]

Is there an app or online calculator that shows field of view for kit like a C8 + Lodestar C + focal reducer? I found this graphic of an MFR-5 focal reducer used with a C6 and Mallincam. The FOV varies with spacers used and also position of spacers between two focal reducer elements.

http://www.mallincamusa.com/Updates%20-%20July%202005/MFR-5.htm

My primary aim is detecting H400 galaxies I otherwise wouldn't see under light pollution, so I'm wondering what focal reduction is best for that goal.

Thanks again fro all the input.

[Martin Meredith]

Try http://www.12dstring.me.uk/fov.htm

Martin

[ollypenrice]

There are lots. I use SkyMap Pro out of long habit but you can model chip sizes and focal lengths on the free programme Stellarium, I believe. Mocking up the image like this is the first thing I do at the preparation stage. I dare say it is for most people. It's also good for planning mosaics.

Olly

[kwjohnson]

Thanks Martin and Olly. Both suggestions help this non-imager understand what I'm looking for.

[steppenwolf]

I do the same as Olly but using the free software Cartes du Ciel. Here is a typical example showing the framing that I would have selected for imaging The Pelican Nebula with my FLT 98 and focal reducer with my QSI 683 CCD camera. Rotating the overlay to get the right angle is simply done by typing 'Shift C' and then using the left/right keys to rotate the rectangle to suit. The example below represents a rotation angle of 250°:-

[Owmuchonomy]

I'm coming at this very late but does this help you?

http://www.12dstring.me.uk/fovcalc.php

Apologies if I'm off track, still on my learning curve!