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Advice please on set-up for 130P-DS Clone


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Hi,

In the land down under we don't seem to have the Skywatcher Explorer 130P-DS and instead have the Sky-Watcher BKP 130 OTAW Dual Speed, and after perusing the specs the only difference seems to be in the name.  http://www.sirius-optics.com.au/astrophotography/astrophotography-optical-tube-assemblies/skywatcher-130-650-photo-reflector.html

I'm still in the early stages of this nocturnal sky gazing affliction, but have a reasonable background in terrestrial photography, my main interest being bird photography. At this stage I have a Nikon D800 full frame DSLR and a selection of lens from 14mm to 420mm which I've used with a tripod to get some encouraging results. My bird photography was a lot to do with sharpness and detail and this led me to look for the same in my night photography. To this end I acquired a new EQ6 mount which I've upgraded with the stepper motors and the SynScan v4 handset. I've more or less come to grips with the mount.

Scanning the forum for snippets of info to help me on my way I came across this thread and to be honest, I found some of the posts to be mind boggling.

How the hell can you get those shots from a 'cheap' telescope? For that sort of money a 'cheap' camera lens would give you fairly 'nasty' results.

OK, I want one, or the local equivalent. These are it's specs:

Dual-Speed 10:1 ratio focuser Optical Design Parabolic Newtonian Reflector Diameter / Aperture 130 mm Focal length 650 mm Highest Practical Power 260x F/Ratio f/5 Finder Scope 6x30 Focuser Diameter 2" Eye Piece 2" Tube Weight 3.66kg Tube Dimensions 16.0x61.5cm3 Shipping Weight 8 kg Faintest Steller Magnitude 12.7 Shipping Dimensions 67x29x26 cm3

Now this is where my limited knowledge of things astro hits the wall. I know I'll need some sort of Nikon specific adapter to mount the camera to the scope and hope the scope mounting point can handle around 1Kg. Also from reading the above it seems like the 6 x 30 finder scope is not an option for guiding so I guess that will need to be replaced, or not. And then what do I need to attach the scope to my mount. This is a pic of the saddle on my mount.

I should state here that I'm an OAP (Old Age Pensioner) so not exactly flash with cash, but I won't go the 'cheap 'n' cheerful' route if it won't do the job.

If someone could give me a rundown of the basic bits to get me started I'd appreciate it.

Thanks for reading all my waffle.

 

 

EQ6  Saddle SGL.jpg

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Hi Kev

the good news is that the link you provided appears to be the same down under version of the 130 PDS. I picked one up recently second hand for £100 including extras. The bad news is that you should try and pick the critical bits out of the huge thread you spotted, no mean feat. Anyway, here are a few thoughts from my recent attempts with this scope.

1) you will need a coma corrector. I use the latest Baader version. This will improve your chances of getting a flat field.

2) you will need a Nikon specific T adaptor to attach your camera body to the coma corrector. You say you have a full frame camera. I used an APS-C sensor Canon so you may find you get some vignetting with that size chip

3) the spacing from chip to coma corrector is critical. You may have to experiment but I find I need about 11mm between camera body and coma corrector. I use a T2 extension ring for this

4) get a Bahtinov mask for the scope to aid focusing

5) for guiding I use an Altair Astro maxi guider package and a lodestar guide camera but there are cheaper options

the scope comes with a dovetail bar fitted so will fit your mount saddle.

Then you will have to get to grips with all the software etc etc.

others will come along and chip in. Have to go now.

Edited by Owmuchonomy
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Oh, and you will need a means of collimating your scope.  I use a Cheshire collimator to assist with this.  Others prefer laser collimators but I don't see the point in one of those as you need to collimate that too to be sure of alignment.

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2 minutes ago, Owmuchonomy said:

Oh, and you will need a means of collimating your scope.  I use a Cheshire collimator to assist with this.  Others prefer laser collimators but I don't see the point in one of those as you need to collimate that too to be sure of alignment.

Aha, collimation.

How often does that need to be done?

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How long is a piece of string?  For astrophotography I would check it every time I use it.  It shouldn't need more than a bit of fine tuning on the primary mirror though once you have set it up initially.  Here is mine on the shelf behind me so you can see the guiding set up attached.  I also did the extra focuser screw mod that is recommended.  This helps get good image train alignment. I have only used it once since I got it (January) due to clouds!  I'm going to make a Baader film solar filter to go over the 2" port so I can have a white light set up for the transit of Mercury.

IMG_0369.JPG

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Ok.  In the meantime here is the Baader MPCC, T2 extension ring and Canon T bayonet adaptor (M48) I have used and then 2nd picture screwed together.  This then drops into focusser on the scope.  CCD cameras are beyond my ken but I know spacing becomes an issue.  Read the monster thread about that because it is necessary to modify such that you can get the MPCC internal to the focusser I believe otherwise you run out of back focus.  I don't have this problem with a DSLR.

IMG_0370.JPG

IMG_0371.JPG

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Chris, now you are doing my head in.  :icon_salut:

I had to google MPCC to find out what you were referring to.

I though I had my foot on the first rung of the ladder, now I'm not real sure i can even see the bloody ladder.

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Hi Kev,

The 130PDS is capable of some stunning images which belie its cost, however, it will benefit from some "tinkering", and some things will need to be added to your setup.

  • Guiding - pretty much a requirement for long exposures.  I have modified a finder scope taken off the eypiece and replaced it with a camera, the one that comes with the 130 is possibly too small I have a 200 P as well and that finder seems to suit (9x50), it has the same connector so that made things easier. with a 650mm focal length flexure etc are not too troublesome
  • Collimation - Go read Astrobabies guide http://www.astro-baby.com/collimation/astro babys collimation guide.htm, then read it again :icon_biggrin: - make sure you understand before you go near the scope, and when you do go slow.  It can be an easy path to get lost on and until you have it down pat can be less than intuitive.  Once its done, it takes minutes at the start of a session.  One small hack  is to put a steel washer between the secondary support and the spider.
  • Coma corrector - as said this is required to get a flat image.
  • Polar alignment - whilst you don't have to be perfect for a couple of minutes exposure as your times go up so does the need for accuracy - might as well learn to get it right :wink2:
  • I found I needed to fit an "end cap" to the back of mine to stop stray light entering around the primary, some people just put a shower cap around the back of the scope.  I have a piece of model board cut out and held on with some velcro.
  • Some counter weights (exercise ankle weights seem to work well), the scope is short so when you start hanging cameras etc off the front it becomes top heavy quickly.
  • Light pollution filter?

The scope is capable of lots out of the box, but with a bit of attention is even better, the most expensive bits are probably the guide camera, the coma corrector and the light pollution filter - but you would need 2 of these whatever scope you were using.  Most of the other bits are cheap fairly, but really its just an investment of some time, and lots of learning.

Cheers

Ross

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Quote

DarkKnight
Chris, now you are doing my head in

and so it begins! lmao

it will only get worse as you try to progress,going ccd route will get expensive fast and can be a minefield as to which cam is best for your budget,filters,spacers,filterwheels and so on.

get a t2 adapter for nikon this goes on where you would put a lens,then that will screw onto the focuser of scope,use a remote to activate the camera to minimise vibration

best to start simple,then if you feel this is for you then save and go all out on the ccd route

would avoid the collimation pitfall until you have posted pictures,others can tell you if you need to collimate

many new to this hobby buy the scope then dismantle it and are left well and truly stumped by the process of collimation

its easy after you have done it a few times,but if it aint broke dont fix

with camera in manual, select an iso of 800/1600 and expose for 5-10 seconds,see what the picture looks like,check for trailing

use livewiew to focus best you can

always ask on here if you are stuck,someone will always try to help

as for polar aligning ,with you being down under drift aligning would probably be better

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Thanks for your input Ross.

It's very helpful and most appreciated. It seems the general consensus that the scope needs a bit of a fiddle.

SF, you raise some pertinent points about jumping into a CCD camera straight up. I'm fairly comfortable with DSLR's so it is probably prudent to stick with what I know in the early stages.

This forum is a great source of knowledge for those like myself that know Jack, and also gratifying for the willingness of those that do to share.

Thank you.

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3 hours ago, Owmuchonomy said:

Read the monster thread about that because it is necessary to modify such that you can get the MPCC internal to the focusser I believe otherwise you run out of back focus.  I don't have this problem with a DSLR.

 

Dont worry, you only need to consider internally mounting the coma corrector if you wish to avoid "cutouts" in stars (where the focuser cuts into the light path). I wouldnt pay too much attention to that at the moment as its just an asthetic thing, and can be tackled further down the line.

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3 hours ago, DarkKnight said:


Chris, now you are doing my head in.  :icon_salut:

I had to google MPCC to find out what you were referring to.

I though I had my foot on the first rung of the ladder, now I'm not real sure i can even see the bloody ladder.

Sorry, this hobby is littered with acronyms. I should have explained it a bit better. I see Rob has joined in so I can sit back and relax whilst he answers queries more comprehensively. ? Note his point about a cut out or bite out of your stars. I get this with my set up too but it's very minor and as he says can be sorted down the line.

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Another dumb question.

As as photographer I generally prefer natural colour to monochrome, and I was surprised to see that mono CCD's were generally dearer than the colour CCD's.

Doesn't seem logical to me as the colour sensor also captures black and white plus red, green and blue. Do I need to do a crash course on CCD sensors, or is there a simple explanation?

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Short answer and my understanding, light in this hobby is at a premium, if you have a sensor with colour in it only half the sensor picks up green and a quarter each to red and blue.  With monochrome and colour filters 100% of the sensor picks up each colour so is more sensitive.  Also if you think about it a 20M red image where neither green or blue is triggered is full of holes with only a quarter of the sensor detecting anything, debayered that makes it a 5M image.

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34 minutes ago, DarkKnight said:

Doesn't seem logical to me as the colour sensor also captures black and white plus red, green and blue. Do I need to do a crash course on CCD sensors, or is there a simple explanation?

One-shot colour CCDs are convenient but mono CCDs offer superior performance and greater flexibility. Shooting luminescence data (with no filter) followed by RGB (through coloured filters) allows a deeper image to be taken in the same amount of time. They can also be used with narrowband filters. Physically, all CCD and CMOS sensors are mono, the colour versions have a Bayer Filter in front of them.

AP is quite a learning curve but it does start to make sense after a while. You've invested in a good mount, have you considered putting your camera directly on it to get up and running? Everything is more forgiving at short focal lengths and camera lenses are typically faster optically than scopes.

10 hours ago, DarkKnight said:

How the hell can you get those shots from a 'cheap' telescope? For that sort of money a 'cheap' camera lens would give you fairly 'nasty' results.

I've used sub-£20 second-hand camera lenses from the 1960s with good results. :)

Edited by Knight of Clear Skies
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4 hours ago, DarkKnight said:

Another dumb question.

As as photographer I generally prefer natural colour to monochrome, and I was surprised to see that mono CCD's were generally dearer than the colour CCD's.

Doesn't seem logical to me as the colour sensor also captures black and white plus red, green and blue. Do I need to do a crash course on CCD sensors, or is there a simple explanation?

You can pretty much throw the (daytime) photography rulebook out of the window when it comes to astro imaging! Youre going from a medium plentiful in light, to one where the light you are caputuring has been travelling for possibly billions of years. It wont be long before you start looking into quantum efficiency, well depths and read noise ;)  ..... and noise is half the battle. A CCD trumps a DSLR in terms of noise too - with no sign of the dreaded chromatic noise that plagues OSC (colour) cameras.

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Thank you sidelight, Knight of Clear Skies and Uranium.

I did a quick refresher course on Bayer filters and it all makes sense now, sort of.

Sidelight, an interesting observation on debayering.

Knight of Clear Skies, shame you are too far away for a shooting session. With your clear skies and my darkness, we would have perfect conditions.  :thumbsup: And I agree that with lens, cheap doesn't necessarily mean crappy. One of my favourite shots was taken with a Pentax M 50mm f1.7 from the 70's. I still have it even though I switched to Nikon about five years back. And yes, I've been doing some testing with the camera on the mount with mixed, but encouraging, results.

Rob, it's scary to think that some of what we see in the sky is no longer there, and ceased to exist eons ago. At the moment I'm like a kid in a lolly shop, so many temptations, and absolutely no idea of what anything tastes like. I think, as the Knight suggested, I'll continue with my camera on my mount till I've come to grips with that set of challenges, exacerbated by no view of the SCP, and when I feel I'm ready for a scope probably start with a modded DSLR.

Thank you all for taking the time to help a newbie trying to find his feet in this rather daunting photographic genre.

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Nowt wrong with using a lens for now, a decent 50mm lens can take some good pics. But an EF 100 or 200mm prime lens is even nicer ;)

Actually, im think of sticking the 50mm on the CCD camera sometime this Summer to see what it can do (perhaps some wide shots of the galactic centre).

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Hi Rob,

I actually have a fair selection of lens, from the Samyang 14mm f2.8 up to the Nikon 300mm f4 + 1.4 T/C.

This is one of my earlier shots with the 14mm, not spot on for focus and too long on the shutter, but it gave me enough encouragement to go further. (ISO4000, 30secs at f2.8)

PS: There is a general photography consensus that there is more recoverable detail in an overexposed shot than an underexposed one. Does this apply in astro photography?

 

 

DSC_4445 - Copy - Edited - Less blue.jpg

Edited by DarkKnight
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On 13/04/2016 at 22:51, DarkKnight said:

Hi Rob,

PS: There is a general photography consensus that there is more recoverable detail in an overexposed shot than an underexposed one. Does this apply in astro photography?

 

Properly exposed shots have even more. :icon_biggrin:

Err on the side of longer exposures but don't over expose, camera histogram peak 20>40%.

 

Edited by wxsatuser
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There are arent that many objects that can overexpose/burn (eg: M42, M31 core, PN's etc) - but on the majority of stuff you can just go for as long as is reasonable (600s is a good average to aim for). The only danger with a DSLR is that long exposures burn out the star colour quite easily (dependant on your ISO), and the longer you expose - the more thermal noise you will generate.

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