astrophotography with Nexstar + SLR

[nanoman]

Hi - i am new to SGL and pretty much a complete novice. I purchased a Nexstart 4SE late last year - its a great unit but i have been, in general, very disappointed with what i can see. I general i see only a touch more than i can see by eye (everything but the moon is a tiny white spec). Light pollution is very minimal. Assuming i had been very nieve in thinking i could see anythiglike the detail i see in web postings i have spoken to the manufacturers. According to them i should be able to see a great deal more than that. I have bolted a Canon SLR onto the T adaptor at the back of the telescope hoping that long exposures would be the key but all i seem to get is noise or blurred specs. Any advice would be very very welcome. I have seen some stunning images of Jupiter and galaxies posted and would much appreciate advice as to whether it is ridiculous for me to seek the same.

JJD

[ianporter13]

JJD,

Astrophotograpy can be very frustrating and takes time to master.

if you're getting 'blured specs' then it sounds like your focus is out, it is very tricky to get good focus with a dlsr at the best of times. I'd take a shortish exposure (3 seconds or so) of a bright star then zoom right in on the preview screen to check focus, keep doing that until you've got the best focus you can then go for a longer exposure

I would suggest that the nexstar 4 is not the easiest if scopes to use for long exposure dslr images and that you may be better of starting with a webcam and trying imaging the moon and planets.

you need to keep in mind that the images you see posted may have taken the imager years to reach the point where they are getting great images.

don't give up, just take your time and start with easier bright objects.

Ian

[EA2007]

Hey there,

I too have the NexStar 4SE (although I am selling it in a few weeks) and it is not the ideal scope for astrophotography. That said however, you can manage somethings from it and in my opinion its down to just a few things:

-Power supply

-Focus

-Alignment

and

-Camera

The power supply must be coming from a continuous source i.e. a power tank or mains adapter. The in-built battery compartment is a waste of space and I think that Celestron should have designed the scope better here to perhaps accomodate some stronger motors or a more sturdier fork arm instead ofgiving a battery compartment that uses 8 whole batteries in about 5 minutes.

NOTE: The plastic (why oh why Celestron!!) fork arm is very prone to vibration, indeed the shutter release on my SLR is enough to wobble the scope. I can remove some of the vibration by having the scope's legs at their lowest point and by hanging my 12V powertank from the accessory tray, but the problem is still quite noticable. So your blurry star images are similar to what I recieve. However keep with it as some exposures you take will show no blurring.

Focus must be spot-on, I images M13 last year and my focus was right off, like Ian said, try imaging a bright star and get that focused first then move onto your DSO subject. However saying that, focusing a dSLR isn't easy-why can't all dSLR's feature LiveView!

Alignment, I assume that you have the wedge alignment done, this makes a huge difference to not only images but the tracking on the whole. From my experience taking the time to do a proper alignment is crucial to good tracking. The use fo the wedge not only iliminates field rotation but provides far better tracking than using the NexStar in Alt-Az.

The camera has to be upto the task, unfortunatly I purchased an OIlympus dSLR and its bad for astrophotography as it will only expose for 1 minute on BULB mode with an ISO of >500. Given that the NexStar is an f/12 scope then long exposure imaging with my camera is basically out of the question. So you ideally need a dSLR that isn't an Olympus, which can expose for as long as you need.

If you have all of the above set up okay then you may be able to gain a few good images, try getting the best out of your equipment before you give up though! I have found that there are some areas the 4SE is good in and others which it isn't. Planetary observations are great, Saturn appears the same size as in my 8inch Newtonian but with more contrast. Jupiter is the same although it is brighter in the NexStar, and I can only get the cloud banding with my 8" Newt.

The problem arises with DSO's. Obviously the NexStar is only 4inches in aperture and has a narrow FOV so relitively faint DSO's such as M81+82, M51 aren't that possible in my experience. Brighter objects such as M42, M13, M44 and M45 are possible as these are bright nebulae and star clusters. I have managed to get M57 and M27 and indeed imaged M57 last summer but I needed way more images to be able to stack for a decent image.

If I were you I would wedge-up your scope and try M42 before its completely lost for summer, you can always take smaller exposures, say of 2 minutes and then stack them in programs such as DeepSkyStacker and then mess around with it in Photoshop.

[nanoman]

Hi - many thanks for these replies - much appreciated. Predictably, your replies raised some more questions.

I am not using a lense on the SLR - it is directly attached to the T mount on the back of the Nextstar - there should be, then, no SLR focussing. I am using a remote trigger to photograph in order to minimise vibration.

What is "wedge alignment"?

Is stacking simply a superposition of digital shots in order to improve S:N?

Is the suggestion that i really have to spend more than $700 to see much more than the human eye?

JJD

[ianporter13]

with the SLR attached to the scope via a T -mount the scope itself will need to be focused so the image come to focus on the sensor, this is done in the same way as when you focus for an eyepiece.

Stacking can be as simple as you suggest although there are some more complex algorithms which can also be used to enhance the image.

Ian

[EA2007]

Lots of questions......I shall attempt to answer some to the best of my knowedge, but you may get better info from other users.

I attach my dSLR to the scope via a t-ring and universal t-adapter (I remove the lens of the camera to achieve prime focus). The t-adapter is 1.25" wide and I slot it into the eyepiece holder. Alternativly you can purchase a threaded t-adapter which (I assume you have) screws into the back of the scope beneath the eyepiece. With the way that I do it then I have to rotate the focusing knob to achieve focus.

The scope in 'normal' mode with the 12V power pack attached:

The back of the NexStar with the threaded adapter hole open:

My Olympus E-400, universal t-adapter and t-ring (note that the t-ring is for a standard Olympus SLR, I had to purchase an OEM adapter which screws into the t-ring and the Olympus camera):

The t-ring and t-adapter (together) which attaches to the Olympus E-400:

The finished article ready to go into the NexStar 4SE's eyepiece holder:

The NexStar with the Olympus dSLR placed into the eypiece holder, not the threaded hole beneath:

The Wedge feature in operation, mine is set up fro 54 degrees as this is where I am at :

The alignment scale pole, make sure that the number you need is level with the base of the wedge:

The scope pointing towards polaris (yes I know its daytime, but its only to show), when performing a wedge align (after a EQ North Align) the scope slews to where it thinks polaris is -MANUALLY move the scope to where polaris is using the red dot finder and altering the scale pole. DO NOT use the goto handset :

Wedge alignement is the process of aligning your scope using the built in wedge with the pole star (polaris). This means that the scope can track at a sidereal rate (the rate at which the stars 'appear' to move across the sky) in only Azimuth thus erradicating the use of Altitude in the scopes motors. If you look at the celestron maunal then it tells you the process but it is quite backwards in my opinion. From what I remember then you have to align the scope in EQ North mode (if your in the Northern hemisphere) using the wedge to place your scope at the desired angle (for me it is 54 degree's whereas Los Angeles is 34 degrees I think. Then perform a wedge align and then perform another EQ North align.

I would ignore whatever someone has said about needing to spend more to get better results. Its down to the user getting the most out of the scope.

Stacking requires taking a set of images say 10 x 2 minutes and then using a computer program to add them together so your final image incorporates the data from each picture. There are many ways of doing it however.

[MartinB]

Slow down Nanoman! I'm concerned that your scope isn't giving you better views than with the naked eye. That isn't right at all. Whilst long exposure photography will show you much more than visual observing a scope should still massively enhance what you can see with the naked eye so something may be wrong. Have you had a look at Saturn? You should be able to see the rings easily. How about M42 - you should be able to see wispy clouds of nebulosity. If you have a look at M3 you should be able to see it looking like a dim ball of cotton wool. With care and patience you should be able to make out individual stars going close into the core. From your relatively dark location you should be able to make out M81 and 82 and differentiate the differences in shape between the edge on M82 and the face on M81. You wont see any more detail that that but the pair still make a great site. Looking at the moon the craters should look so sharp and close that you feel you can almost reach out and touch them.

If you can't see these things then don't try to correct the problem with long exposure astrophotography (unless you want a nervous breakdown).

There may be a problem with your optics - do you get sharp close up views of distant objects during the day (avoiding observing if the sun is shining of course)? If you have a local astro society it would be a good idea to take it along on a clear night and let someone have a look to check out the scope's optics.

You are observing outside with a well cooled scope aren't you?

[ianporter13]

If you have a local astro society it would be a good idea to take it along on a clear night and let someone have a look to check out the scope's optics.

now that's the best advice you can get......

Ian

[EA2007]

now that's the best advice you can get......

Ian

Other than not eating yellow snow!

[ianporter13]

:roll: :roll: :roll:

[nanoman]

Hi - many, many thanks for those replies again. If i understand things correctly, i have all the hardware i need correctly configured and that "wedge alignment" will effetively remove/reduce the blurring effects of the earths rotation relative to the stars? If thats correct why not just use tracking?

I am not sure what is meant by a "cooled scope"? I am outside and its cold - is that what you mean?!

I`ll keep playing - through my Nexstar Saturn is a tiny white spec. The only thing that is in the least bit impressive is the moon!

JJD

[EA2007]

Don't worry too much,

Take things slowly....

The wedge align is purely for better tracking of the night sky, it removes what is known as 'field rotation' when imaging. If you were to take a long exposure image (say, longer than 1 minute) then the object within the field of view (FOV) will appear to rotate over time, your final image will look blurred in one direction, hence field (the view) rotation. The wedge feature as far as my experience goes is better for both photography and tracking as it eliminates the errors that can occur when the scope is moving in both the altitude (up+down) and azimuth (left and right), when your using the wedge the scope is only using one of the motors to move so the chance of any errors in tracking is reduced.

In reply to the 'cooled scope' phrase, basically all that is meant by this is that your telescope needs to be at a similar temperature range of the air in which you are using it. So if you are outside with your telescope and its cold (say 2 degrees) but you have just moved your telescope from inside your house where its nice and warm (say, 15 degrees) then there will be a massive difference between the scope's temperature and the ambient temperature of the outside air.

All telescopes require different 'cool-down' times. From what I gather, open scopes like a newtonian require less cool down time than a housed refractor or Schmidt/Maksutov Cassegrain. This is because the outside air cannot get into the scope due to the lenses, so additional time is required for the scope to cool down. I allow about 30 minutes for my newtonian, but the longer you wait the better it gets. For the NexStar it can require a bit longer. Basically the air currents withing the scopes tube affect how well you can see an object, its like looking at the heat wave on a road in summer, objects on the horizon appear to shimmer. You will get loads more detail in a DSO (deep sky object) if you allow you scope to cool down.

With regard to Saturn, I don't want to be rude but perhaps you are maybe looking at the wrong thing. I know that right now Saturn is close to Regulus in Leo so maybe you are aimed at that instead, if I remember rightly, Saturn is to the left of Regulus.

[John]

Hi JJD,

I think MartinB's advice is good - get the scope performing well when used visually before trying to use it for astrophotography.

By a "cooled scope" we mean that the scope and it's optics have had time to ajust to the outside temperature as you will not get good images until that has happened. Cooling can take an hour or more with the Maksutov type scopes (like yours).

You don't say which eyepieces you have tried - with a low power eyepiece (the one with the highest focal length in mm marked on it) Saturn will look very small. With a higher power eyepiece you should see quite a nice image - it will still be quite small though - not like the images you see in magazines and all over the web though

Try using the low power eyepieces on objects like M42 in Orion - that should look nice.

Astrophotography is an exacting business and it is best to take some time to master your scope visually before jumping in to imaging !.

John

[blueranger]

Hey there,

I too have the NexStar 4SE (although I am selling it in a few weeks) and it is not the ideal scope for astrophotography. That said however, you can manage somethings from it and in my opinion its down to just a few things:

Sorry to hijack your thread Nanoman, but I just wanted to ask EA2007 his honest opinion (and indeed yourself) on the 4SE.

I was contemplating this as my first scope and was slightly worried about hardly seeing Saturn as this is supposedly one of the best subjects and as most shop owners seem to think you get a good view of it through the 4SE.

When all's said and done, as a new astronomer, would the £500 pound (with eyepieces etc) be forgotten about once seeing some of the views possible.

Sorry once again but I need an honest opinion!

Regards,

Blueranger

[EA2007]

Blue Ranger,

The scope sells for around £340, so with your £500 you can afford to get either a 2x or 3x barlow lens and perhaps some other eyepiece's.

In my honest opinion and from using it just last week on Saturn then I can say that it is good enough for a beginner. I haven't tried the 4SE witha barlow lens, only the supplied 25mm EP. The image of saturn is quite small but you can make out the rings and possibly the cassini division but that may have been a distortion with my focusing.

In my opinion Jupiter is a far better subject because it is so much larger and you can see the moons more clearly, that said though there are issues with veiwing the cloud bands on Jupiter, but with a barlow you should be able to make them out. Other views with things are good, M42 looks good, as does M45 etc etc, especially star clusters. The rather high focal ratio can dim down some fainter DSO's such as M51 and M101 and the FOV is a little narrow but you shouldn't be expecting lots through a 4 inch mak. anyway.

In terms of use though, its far easier to set-up and use that a TAL 150. Its fairly small aswell so you can get it in the boot of your car no problem.

If your wanting to try some basic imaging then perhaps get an EQ mounted scope, the 4SE does have the wedge but an EQ mount would be better suited....it all depends on your money situation and what you want.

[blueranger]

Thanks for the reply EA2007, but I bought the Skymax 127 supatrak yesterday!! A slight change of plan, but I took advice from here a went for optics rather than electronics.

Views are good, though I am having a little trouble with the auto-tracking at the mo, but hopefully with time I might get the hang of it :?.

Thanks again.

Blue Ranger.

[mikehab]

Hi,

I know this thread is way old (2008) - but it's still very relevant as far as I'm concerned since I bought a 4SE a couple of months ago and have been playing around with astro-photography - both using a web-cam and a DSLR for planetary imaging so far.

I will be going on holiday later this year to the deepest depths of France where there is absolutely no light pollution what-so-ever - and the skies are always so dark and clear that you can easily see the milkyway clearly with the naked eye - so I'm looking forward to taking the 4SE this year and hoping to capture some really good astro-photos.

I've seen lots of articles from people saying the 4SE isn't really the best scope for DSO imaging due to is long focal length (1300mm), narrow field of view and slow speed (f/12?) ... however I've equally seen lots of other posts from people who have clearly demonstrated that with proper alignment and a lot of patience, it can be done with the 4SE, with good results - and of course it comes with a wedge-mount which helps with the polar-aligned tracking etc.

So - finally - to my question...

What would be the best way to image some DSOs with the 4SE? Would it be better to connect my EOS DSLR directly to the scope's primary focus using a T-mount - effectively turning it into a 1300mm lens (albeit with a narrow FOV), or would it be better to piggy-back the DSLR on top of the scope - effectively using the mount purely to track and using a standard camera lens. If piggy-backing the DSLR - what would be the best focal length lens to use -18mm/28mm/55mm for the widest possible FOV (but unlikely to have anywhere enough magnification to see anything interesting presumably), or something more powerful like a 250mm lens?

Or am I completely wasting my time?

Any thoughts/views/experience most welcome...

Thanks,

Mike