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  #21  
Old 02-04-2013, 09:26 PM
bloodhound31
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Originally Posted by Shiraz View Post
a Powermate is a Barlow with 2 extra lenses that make it telecentric. there is no real difference in this application, except that a Barlow can give you varying magnification whereas a Powermate is specifically designed so that it doesn't.

With a 618, the rule of thumb suggests that you need about 4x for your scope - just like http://www.astrobin.com/users/FranckIM06/

suggest a 3x Barlow with a short extension - that will allow you to vary the magnification to suit the seeing.
Thanks mate. What do you mean by extension? Link? Picture of one?

Does the 618 fit into this?

Baz.
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  #22  
Old 02-04-2013, 09:36 PM
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yep, also fits into this at about 1/3 the price and the same result

http://www.bintel.com.au/Eyepieces-a...oductview.aspx

typical extension tube http://www.bintel.com.au/Accessories...oductview.aspx
but it doesn't work with a Powermate
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  #23  
Old 02-04-2013, 09:52 PM
bloodhound31
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Originally Posted by Shiraz View Post
a Powermate is a Barlow with 2 extra lenses that make it telecentric. there is no performance difference in this application, except that a Barlow can give you varying magnification whereas a Powermate is specifically designed so that it doesn't.

If interested in details, this is a good summary on Barlows and telecentric Barlows - http://www.brayebrookobservatory.org...BarlowLens.pdf

With a 618 camera, you need a final FNo of about f28, so you want about a 4x magnification Barlow or Powermate for your scope - just like http://www.astrobin.com/users/FranckIM06/

suggest a 3x Barlow with a short extension - that will allow you to vary the magnification to suit the seeing. If you do get a Barlow, buy a good quality one.
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Originally Posted by Shiraz View Post
yep, also fits into this at about 1/3 the price and the same result

http://www.bintel.com.au/Eyepieces-a...oductview.aspx

typical extension tube http://www.bintel.com.au/Accessories...oductview.aspx
but it doesn't work with a Powermate
I see. When you say, "vary the magnification to suit the seeing." What do you mean exactly?

Do you think the televue 3x barlow is good quality?
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  #24  
Old 02-04-2013, 10:00 PM
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if you have high frequency jitter due to seeing, it sometimes helps to drop the magnification a bit and decrease the exposure times to freeze the seeing - eg you may drop back from 4x to 3x and decrease the exposure time from 1/60 to 1/90 sec per frame.

from my experience all televue stuff is top quality. I have the TV3x, a TV2x and a 5x Powermate - they are all so good that they provide magnification and nothing else and they work down to f4
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  #25  
Old 02-04-2013, 10:05 PM
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Originally Posted by ezio49 View Post
Does anyone of this forum help me?
Thanks
Ezio
I don't want to be rude mate, but you need to start your own thread, that way people don't get confused answering two different lines of questioning.

That would be a better way to get help.
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  #26  
Old 02-04-2013, 10:07 PM
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Originally Posted by Shiraz View Post
if you have high frequency jitter due to seeing, it sometimes helps to drop the magnification a bit and decrease the exposure times to freeze the seeing - eg you may drop back from 4x to 3x and decrease the exposure time from 1/60 to 1/90 sec per frame.

from my experience all televue stuff is top quality. I have the TV3x, a TV2x and a 5x Powermate - they are all so good that they provide magnification and nothing else and they work down to f4
Thanks Ray, you have been very helpful indeed.

I've been out of the loop for more than a couple of years now, so learning all this again is like starting from scratch. Technology, optics and software have all changed very quickly.

I appreciate your assistance mate.

Baz.
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  #27  
Old 03-04-2013, 07:45 AM
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Actually for planetary work there is little difference excepting one. With the 2x you can move the camera away from the elements of the barlow and the magnification will continue to increase. However, with the 2.5x powermate if you move the camera further away (via an extension tube) the image will get smaller. I have used both extensively and don't prefer one over the other. I probably use the 2x more than the 2.5x
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  #28  
Old 03-04-2013, 08:27 AM
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you might also consider the QHY5L-II, same chip as the ASI120MC but costs less then the neximage5- mine did anyway- i got a 2.5X GSO barlow- no regrets, seems just as good or better as mine antares 2X APO barlow
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  #29  
Old 03-04-2013, 08:48 AM
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Baz, if you do decide on a QHY5L2/ASI120, aim for f19 so a 2.5x Barlow is the go. With the Neximage5, aim for about f11, so a 1.5x is needed. A 3-4x will be a match for the DMK618, but too much for either of these chips with your scope.

Last edited by Shiraz; 03-04-2013 at 09:07 AM.
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  #30  
Old 03-04-2013, 11:36 AM
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OK now I'm really confused. So many differing opinions from the experienced imagers.
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  #31  
Old 03-04-2013, 12:13 PM
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Bit like an economists convention eh?

You don't just get "the Barlow" that works on all imaging systems - your Barlow must be chosen to match both your scope and the chip that you decide on - there will be quite different solutions for different cameras and scopes. the rule of thumb posted earlier pulls it all together.

As I see it, with that scope, your options are:

D..K21 618 - well tried and dependable - fairly large pixels so you will need a final FNo of about f28 - get there with a bit under 4x magnification with your scope (suggest 3x Barlow with extension tube). Then you will have a setup much like the one that Franck uses so effectively.

QHY5L2/ASI120 - quite new cameras, but some imagers are producing very good results with them at a bit under f20. these have smaller pixels than the DBK/DMK and do not need so much magnification - with these cameras, a 2.5x Barlow is about right with your scope (suggest 2x with extension tube).

Neximage5 - relatively untried, but has high spec chip - has tiny pixels and only needs a final FNo of about f11. - you can get there with a 1.5x Barlow on your scope.

Last edited by Shiraz; 03-04-2013 at 12:38 PM.
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  #32  
Old 03-04-2013, 12:28 PM
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Originally Posted by Shiraz View Post
You don't just get "the Barlow" that works on all imaging systems - your Barlow must be chosen to match both your scope and the chip that you decide on - there will be quite different solutions for different cameras and scopes.

As I see it, with that scope, your options are:

D..K21 618 - well tried and dependable - fairly large pixels so you will need a final FNo of about f28 - get there with about a 4x Barlow with your scope (suggest 3x with extension tube). Then you will have a setup much like the one that Franck uses so effectively.

QHY5L2/ASI120 - quite new cameras, but some imagers are producing very good results with them. these have smaller pixels than the DBK/DMK and do not need so much magnification - 2.5x Barlow is about right with your scope (suggest 2x with extension tube).

Neximage5 - relatively untried, but has high spec chip - has tiny pixels and only needs a final FNo of about f11. - you can get there with a 1.5x Barlow.
Thanks again Ray. Big effort mate. Sorry I'm slow to convince sometimes. I just don't want to spend big dollars and get the wrong combination.

Anyone have any reasonable grounds to dispute this? If so, why?
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  #33  
Old 03-04-2013, 01:02 PM
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This is similar to what I have been saying. So long as you can 3/4 fill your histogram with the magnification you are using, then you will get good results. So a 3x barlow with a good quality sensor will get the results you are trying to obtain. You will need several barlows to work with for varying conditions.

Even though mathematically what Ray has shown is correct; in practice frame rates to collect enough frames with low noise cameras is what you want. Each camera responds differently to this problem. Look for cameras with low read noise, deepish wells and good sensitivity. All the ones mentioned fill most of these requirements. To be honest I think the PGR cameras have the lowest noise of any camera and present very high frame rates. This comes at a cost though.
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  #34  
Old 03-04-2013, 03:54 PM
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Originally Posted by Paul Haese View Post
This is similar to what I have been saying. So long as you can 3/4 fill your histogram with the magnification you are using, then you will get good results. So a 3x barlow with a good quality sensor will get the results you are trying to obtain. You will need several barlows to work with for varying conditions.

Even though mathematically what Ray has shown is correct; in practice frame rates to collect enough frames with low noise cameras is what you want. Each camera responds differently to this problem. Look for cameras with low read noise, deepish wells and good sensitivity. All the ones mentioned fill most of these requirements. To be honest I think the PGR cameras have the lowest noise of any camera and present very high frame rates. This comes at a cost though.
Thanks Paul. I spoke with Bintel today on the phone, as the Black Diamond ED 120 I have was from them and they have never steered me wrong.

With all this great information and their advice, I have concluded that the DBK 618 with a 2.5x powermate will achieve the best focal length without serious loss of light reaching the sensor. I may or may not need an extension tube while imaging with the star-diagonal removed. My Starshoot Pro is on the end of the focus tube at full extension to reach focus so hopefully the DBK with powermate should be ok on there too. I have a 2 inch extension tube so I can experiment when the time comes. I also have a very nice 1.25", 2x Barlow, which I can also throw into the mix to experiment.

Thanks very much everyone for your wealth of knowledge and experience. It has all helped me to make an informed decision and at least allowed me to ask the right questions when it comes to finally purchasing today.

God bless ya's all!

Baz.

P.S. Hopefully in a year or two, (maybe less) I may be blessed with enough cash to get myself a nice 14" RC, so I think the DBK will really come into it's own on that. By then who knows, I may even upgrade the planetary camera too.
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  #35  
Old 03-04-2013, 07:36 PM
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Originally Posted by bloodhound31 View Post
OK now I'm really confused. So many differing opinions from the experienced imagers.
So I guess now wouldn't be a good time to mention the QHY IMGOH. This is what I plan to use on an APOMAX 130 f/12 refractor with a Baader FFC.
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  #36  
Old 03-04-2013, 08:14 PM
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So I guess now wouldn't be a good time to mention the QHY IMGOH. This is what I plan to use on an APOMAX 130 f/12 refractor with a Baader FFC.
You are correct. I have ordered.
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  #37  
Old 04-04-2013, 05:23 AM
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Originally Posted by ezio49 View Post
Sorry, I disturved your private conversations. I was convinced this was a public forum.
No, I don't think that is what he meant. Can I suggest as well, start a new thread, outlining your specific questions. You will likely get a better range of responses to your questions, rather than yours getting mixed up with other responses.
Gary
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  #38  
Old 04-04-2013, 05:25 AM
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You are correct. I have ordered.
Baz,
I've watched this thread, contributed even.
Gut feeling is you won't do it, perfectly, in one go anyway. I'd venture to suggest anyone that is doing any form of imaging, lunar, solar, planetary, etc, will take multiple bites at it. You'll find that some times you can go to a 4x and others prime focus is as good as you can muster. Get the basis of a working start and fine tune it from there. The setup that you suggest you have ordered sounds a great way to start.
Gary
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