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Craney

200PDS. Help needed on buying a new 2" Barlow.

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Evening everybody.

I'm fairly new to the site and still gaining experience.  I like astro-imaging and I am presently compiling shots of the Messier objects to start with.

Every now and again I would fancy a bit more focal length to the optical train for prime focus photography with my 200PDS, Canon 60D and HEQ5.  Mainly to get more angular width to smallish DSO's. 

Not wanting to go power crazy and order a 5X monster, I was wondering what is the preferred option in terms of imaging?    I hear the Antares 1.6X 2"  is a good choice.....??

......and that got me thinking..... I have a coma-corrector on the T-adapter which is apparently 0.9X... so do I have to factor this in to the overall magnification.....e.g.  Final = 0.9 x 1.6... or will the new Barlow partially

correct the ill effects of the  coma issue due to a reduced field of view and so negate the use of the corrector ??

 

Any help or experience most welcome.

Thanks,

 

Sean.

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A barlow will negate coma depending on the FOV, and of course what you intend to do visual or photography, what you have to be aware of is the back focus required for astrophotography as adding a barlow could introduce problems . For planetary photography people do use barlow's with no CC as coma is not an issue as there are no stars as such. For deep sky a barlow is rarely used if used at all as a x2 barlow will take an F/8 scope to F/16 so would make but for the brightest DSO painful to capture , for widefield there is no need for a barlow just a CC or CC/FF, as you try to capture as wider field as possible.  HTH

Edited by cosmojaydee
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Thanks Cosmojaydee,

My widefields are OK with the CC.....no problems there. It is objects like M101 and M57 which I can only bring up to a decent size on an image by magnifying with software.  It would be nice to capture it 'wide' in the first place.

Maybe I need a 250mm PDS.....or  an RC.......:icon_biggrin:

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19 minutes ago, Craney said:

Thanks Cosmojaydee,

My widefields are OK with the CC.....no problems there. It is objects like M101 and M57 which I can only bring up to a decent size on an image by magnifying with software.  It would be nice to capture it 'wide' in the first place.

Maybe I need a 250mm PDS.....or  an RC.......:icon_biggrin:

or one of these

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yes..... nice...

Have they got around the large 'image' size by using a CCD instead of a digital ?......that might be my solution...

but aren't CCD's  better for planets ?   I thought a CCD suitable for DSO's would effectively be the same price as buying a Mak-Newt  (?).......Newt-Mak (?).... ie. expensive.

Mak-Newts seem to be favoured by imagers, and you can get sexy Carbon-fibre ones. They seem heavy though for their apertures.

Thanks for the in put.

 

Sean

 

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Unless youre doing planetary, a barlow should never enter the imaging train. If it's all about "filling the frame", try to avoid thinking like that (it a common beginners error). Instead, just crop the image and display it at pixel scale (ie: 100%) - the object will then appear much larger.

There are very few galaxies that would fill the chip of a DSLR (just M31 and M33), everything else will need cropping or framing so you are capturing more than one target in the FOV (eg: Leo triplet).

Emission nebulae on the other hand... there are plenty that will fill the frame, and in many cases (especially with the 200pds) require a mosaic. But.... lets not go there yet ey ;)

Steer clear of a mak-newt unless you really know what you are doing, the 200pds is plenty to be getting on with for now. Here is a "frame filler" example from the 200pds taken with a full frame CCD camera (chip size just a little smaller than APS-C):

30704432511_05568cc723_b.jpg

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Holy-moly...... that's like an oil painting !!!!

Yes... I have gear-fever.  Bigger - better - faster.

I'll keep plugging away.  Some good pin-sharp clear nights would help, and early retirement....  :icon_biggrin:

 

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Steady on there mate ;)  get the basics right first, then you can move forward. First things to nail down are guiding, field flatness, capture and processing. Once you have a settled setup, just change it one thing at a time - as more often than not, wholesale changes can often lead to trouble (ie: if it aint broke, dont fix it!).

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One thing that hasn't been mentioned yet is that  buying the book "Every Photon Counts" by Steve Richards aka steppenwolf on here from Flo the sites sponsor logo at top is full of information that will steer you on the right track.Read it three times and it could save you a bundle I did and that's why I'm visual only though one day I might chance video astronomy maybe.

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Cheers Uranium235,

Yes, wise words.   I do need to get the tracking sorted.  Of late, the cloud  conditions have prevented any more than 90 mins activity at the scope...... which with me equates to about 5 x 2mins captures.

My mount will keep suitable tracking for this time, after which the egg-shaped stars start to appear.  Auto-guiding seems daunting and time consuming in terms of refinement.

 

Cheers Triton.,

I heard a lot about that book.   I will have to check it out.  Thanks.

 

Sean.

 

 

 

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On your original post 2 inch ed barlows can be had from telescope house for £40 odd,Revelation is the brand.

Edited by triton1
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Hi Sean, first things first, it's great to see my old HEQ5 mount feature in your profile picture. I hope all is well with it!?

I picked up a couple of power mates second hand (bit like finding hen's teeth, but if you are patient they come up from time to time). I occasionally use them for imaging and when I do I use the 2x more often than the 4x. I get some good results and overall I think that I get images which are slightly better than zooming in on small objects in processing (although I've not done a 1:1 comparison). 

As already mentioned, you won't need CC with a Barlow (I guess because with a Barlow you are imaging the part of the FOV which is least affected by the coma issue). 

A watch out with the mount and your comment of a 250PDS, with the camera etc added, it will probably be too much weight for the mount. I have a 200 PDS and with camera, guide scope etc it was on the limit for imaging  

Every photon counts is a good read and you'll save the purchase price in making the right equipment decisions afterwards. 

Good luck with the imaging. 

Richard. 

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If you think about using barlows, you would be better of with a TV PowerMate. But as been said before, why not just crop your images.
Buyibg that book will save you a lot of trouble... No need to reinvent the wheel

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