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Mak-Newt on EQ6 vs CPC800 with Hyperstar

Theinvoker

By Theinvoker
in Discussions - Mounts

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Theinvoker

Theinvoker

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Hi all,

I am looking for a new setup which will be mainly used for DSO photography and photometric work and wondering if anyone had compared these two or similar setups?

The CCD will either be a 1/2 inch ir 2/3 inch chip but stuck between the two. They both cost the same once you have added the guide scope / guide cam etc to the MAK-Newt so stuck between the two.

Any advice is more than appreciated,

Cheers,

Theinvoker

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SteveL

SteveL

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Yes, I pretty much have both setups.

Celestron NexStar 8 GPS (forerunner to the CPC, but almost same optics)

and

SkyWatcher 190mm MakNewt on an EQ6

Be aware that the CPC800 route has two problems:

1) It will need to be placed on a wedge to polar align the fork mounted OTA for long exposure imaging, and the standard "HD" Celestron wedge is barely adequate. The alternative wedges that can cope are frighteningly expensive! I know that starizona say you *COULD* do DSO work with the Hyoerstar in AltAz, but if you are going to spend that much money on a Hyperstar unit, why then nobble your results by running in AltAz???

2) the CPC800 is not Fastar/Hyperstar compatible out of the box, and will require an addition adapter from Starizona to allow you to use the Hyperstar in the CPC. ** The installation of this adapter requires the corrector plate to be removed **

The Hyperstar is a monsterous photon collecter. Running at f/2, there really isnt anything to match it, especially if you are looking at getting the version 3 Hyperstar unit. The wide field is very forgiving of tracking errors, and you can get a lot of subs in a very short time, making some very low noise smooth final images.

One downside of the Hyperstar is in fact one of its string points. With the OTA running at f/2, many filters will be operating well outside their normal parameters. My IDAS and CLS filters give colour shift towards the outer edges of my QHY8 because if the increase light cone angle when it reachesthe filter, which in turn is doing "strange stuff" with the bandwidth. Also, at f/2, the bandwidth of the light has been shifted by 6-7nm, so some of the filters wont pass ANYTHING, and some will pass through light it was designed to block.

The MakNewt is a different beast completely, and I havent had enough time yet to really work out its good/bad points. Lets just say i`m wondering what I will be doing with my C11. The MakNewt has an incredibly flat field, and at f/5 has no bandwidth pass issues like the Hyperstar.

If I had to choose one system over the other... I dont think I could! I love both, but then they are different tool for different jobs. The field of view on the Hyoerstar is VAST compared to the MakNewt, so its horses for courses.

You could of course go for an EQ6 and try to find one of the extremely rare C8 OTAs that are Fastar compatible. Then you get the option of using the MakNewt later as well :(

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Theinvoker

Theinvoker

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Thanks for all the advice, alot to take in :( Ive seen a few CF version of the C8 around at FLO and the like so that on a EQ6 (or the maybe the CGEM if reviews are any good) maybe the best compromise. I do like the look of the flat field on the Mak-Newt tho. Might have to see which is the best deal after christmas :D

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FLO

FLO

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Ive seen a few CF version of the C8 around at FLO and the like so that on a EQ6 (or the maybe the CGEM if reviews are any good) maybe the best compromise.

There are a few Celestron C8 XLT CF remaining at silly/cheap clearance prices but they have the larger Losmandy-type dovetails so you would need to upgrade the EQ6 saddle.

The new Celestron CGEM GOTO mount would also need a new saddle. Edit: I was wrong, it is fitted with a Losmandy saddle so will accept the C8 XLT CF without modification.

HTH

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Theinvoker

Theinvoker

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One thought, if you are thinking of doing photometry isn't the FOV and speed of the scope much less of an issue? Are you getting a non antiblooming gate CCD?

Yes for the phtometry its not a problem, pretty much any decent scope will do. What CCD I get will depend on budget as always but it will mainly be relative photometry to start off with at least so shouldnt be too much of a problem (plotting / searching for eclipsing binary systems etc) so a wide field of view wouldnt hurt as can run more stars per frame.

There are a few Celestron C8 XLT CF remaining at silly/cheap clearance prices but they have the larger Losmandy-type dovetails so you would need to upgrade the EQ6 saddle.

I think if I decide on a C8 I will grab one of them first even if I havent got the money for the rest. Even with the extra saddle price it wills till save me £300 odd compared to the hyperstar conversiuon kit :(

How do people get around the change in wavelength for the filters when the hyperstar is used? That would be the main thing putting me off this option.

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FLO

FLO

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I think if I decide on a C8 I will grab one of them first even if I havent got the money for the rest. Even with the extra saddle price it wills till save me £300 odd compared to the hyperstar conversiuon kit :D

It is also £200 cheaper than a regular C8 XLT! Even I bought one :(

How do people get around the change in wavelength for the filters when the hyperstar is used? That would be the main thing putting me off this option.

SteveL recently experimented with a not-so-narrowband Baader 35nm HA filter, I think the results are somewhere here on SGL.

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ngc2403

ngc2403

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the only way around the band pass thing is to get a curved filter and as far as i know they don't exist.

quick question? are you doing absolute or relative photometry? cause the non-reflection coatings on both scopes can be a big problem for broad band photometric measurements.

Are you going with 8'' aperture? or do you plan to go larger? Just because the scope has a large FOV doesn't mean more stars.

If you had to scopes at the same f/ ratio but different aperture, then pointed at any average part of the sky they will see the same amount of stars.

the smaller one will search a wide but shallow field while the larger will see a narrow deeper field.

In the long run the larger aperture will see more stars as you move it a round the sky. it just might take longer to do each part of the sky.

and finally the hyperstar is very short focal length optical setup and you will probably find that you can't do the photometry on any of the globulars or tight open clusters.

ally

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Theinvoker

Theinvoker

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It will be relative photometry, would love todo absolute but as you say coating etc would play a part and would need alot more expensive CCDs and so on which makes the price rack up quite quickly. Initially I will be searching for eclipsing binaries, most have been documented but you never know may find a long period orbit in there somewhere and good to keep my eye in.

I would mainly use the hyperstar system for taking pretty pictures of dsos, then when Im doing the more scientific work swap it back to a normal setup.

Im not fixed to any apature, have been looking at second hand 10" LX200's as well as refractors along with these two, its trying to find a good balance between the uses really so any ideas are more than welcome :(

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narrowbandpaul

narrowbandpaul

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trust me when I say absolute photometry doesnt require an expensive CCD....ally and I used an ancient SBIG ST7, which is the biggest pile of carp i have ever used...and we have good results...

heres how I would do it....

get your 8/10" SCT and a CCD with the Sony ICX255 chip (sensitive from about 400-1000nm, which covers BVRI Johnson filters). The drawback with this type of camera is the low well depth of the Sony sensors....but it would be a good start (27500e- approx).

Then get a set of Johnson BVRI filters ( they will come in a set with the U filter, but a) the atmosphere is carp in the NearUV and :( the poly electrodes absorb UV photons..so the U filter may be of very limited use, but BVRI is definately fair game.

These will be expensive, around £500, but you only need 1.25" so they may be less than this.

Take a set of exposures through each filter...apply darks and flats, and then stack to remove noise. Make sure the star of interest doesnt saturate (reach near 65535) or the photometric value is lost forever...a value of 40000ADU will be about right (the antiblooming gate kicks in before full well)

you can find the quantum efficiency from t'internet and you can measure the gain of the ADC through experiment (this converts the ADU (analogue digital unit) to electrons, which are a meaningful quantity)

this allows you to work out the number of photons per second...multiply by the energy of the photons...this gives joules per second, or Watts. Divide by the area of the telescope aperture, this gives watts/square metre....or Flux...which is used to derive a magnitude...

this gives you a professional setup for photometry...using the same filters as pro observatories.

just a thought...something to work towards perhaps

good luck

paul

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Theinvoker

Theinvoker

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I have used research grade custom scientific filters in the past and they are decent. SCS sont seem to have them might email them direct and see if I can find a supplier :(

PS as a side note: they also can supply custom filters tuned for F/2 imaging systems so anyone with a hyperstar and money burning a hole in their pocket might be worth giving them a call!

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narrowbandpaul

narrowbandpaul

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i saw cust sci's filters for fast optics option....should cost a pretty penny but some of the best imaging available is open to you....great filter that allow of bandpass shift and fast optics that collect those photons from weak lines very effectively.....

so you liked the cust sci?

andovercorp.com also do them. Not sure of price but they make every filter under the sun

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ngc2403

ngc2403

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As Paul was saying, absolute photometric measurements are not out reach for amateur astronomy, so don't sell yourself short.

We didn't do the photometry in the way that Paul described tbh, we used a low resolution grating to produce a spectrum and then after calibration we got some filter transmission curves and convoluted the spectrum with the filter curve to find out how bright each star is in each filter.

it is not prefect and needs lots of preparation and some computational software to get the results, however if you have the software then you just need a £80 grating!

To do this you need to have a setup that it not well past the seeing limit of your sky .

anyway your plans sound very interesting and i would love to learn work about how it all works

ally

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Theinvoker

Theinvoker

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anyway your plans sound very interesting and i would love to learn work about how it all works

Will do :( Hoping to get a spectrometer at some point too but cant find any UK suppliers. Im sad and like looking at pointy lines lol.

Oops! have just heard that the Celestron CGEM is fitted with a Losmandy saddle, as is the Celestron CGE mount, so will accept the Celestron C8 XLT CF without modification.

Ack that makes it more complicated. Was almost set on the Mak-Newt. Guess see what the CGEM is like and what fits the budget when all the moneys in. They both seem like decent enough setup for my needs so dont think I will go too far wrong either way :D

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