Long Exposures

[sabana]

I want to do long exposures of deep sky nebulaes and planets. All I have is a Nikon D40. I have a AZ mount and a 8 inch refractor. Will I be able to capture anything over 30 seconds? Will I need an GEM and a webcam?

Where do you get long exposure webcams from? I can't see any on the internet.

Many thanks

[Digz]

Firstly welcome to SGL sabana, you will find a wealth of knowledge and expertise together with people willing to share it.

To answer your question you are going to need to consider the following:

A remote release for your camera to allow you to use the bulb mode

A T thread and adapter to connect to your scope

A way of making the scope track the apparant motion of stars.

In a simplistic way you should be able to get around 30s exposures if you can sort out the above with an AZ mount.

DSLRs are a cheap way to get a big chip for astrophotography (AP) and can be used for nebulas etc. For planets people tend to use webcams with there small chips and associated crops allowing you to capture planets at an apparant greater magnification (be warned though you may very well need to throw a barlow into the mix and even then the planet will appear small.)

Im not familiar with the webcam route but have a search on the forums for LX webcam mods. Have a look at the Modern Astromomy website as they do a flashed Phillips Webcam (called Modern Astronomy Planetary Imager).

In basic terms AP is all about the mount. A good GEM mount is the best way for AP, something that is heavy, has a good capacity to carry kit and accurate motors. Most people start with an EQ5.

I would be tempted to say, to get you into AP, to try your AZ mount with your DSLR attached and maybe get a webcam, like the one above, and try planetary stuff. Learn the ropes with this kit, as plenty of queastions here then you can decide how to move on.

HTH

[glowjet]

The answer to your question is yes, a GEM driven mount is essential for long exposure photography and a web cam or DSLR camera, a basic web cam such as the Phillips SPC900 or cameras from such as the Imagingcource company, will cover you for the planets and some DSO, the DSLR will be needed for all other work in the field of DSO. There will be many members who can give you a more in depth answer in this field and I would suggest you have a troll through the Imaging section of the forum

John

[ollypenrice]

Before starting to look into equipping your SCT for deep sky imaging with a DSLR I would strongly suggest you do quite a lot of reading first. Try Making Every Photon Count by Steve Richards, available from FLO the sponsors of the forum.

The SCT is a very difficult instrument to use for DS imaging and needs a large collection of add ons to get it workable. Starting from scratch would be a better and cheaper idea in my view.

Moon and planet imaging with a webcam is a great thing to do right now, though. You don't take long exposures, you take a couple of thousand fraction-of-a-second ones and combine them an a free programme like Registax.

Olly

ollypenrice's Photos

[sabana]

Thanks guys. Very helpful information for me to look at in detail.

One last question. Is it possible to get good results from 30 second or more exposures with a Nikon D40 on a GEM mount with auto tracking. I'd rather stay with my DSLR as I know how to use it manually and if the images are good then thats all I need right now. Or gain can I satck shorter exposures taken from my D40?

Thanks for helping.

[ollypenrice]

For the planets and moon you can get something, especially on the moon. For deep sky the honest answer is 'not really.' Long focal lengths need accurately autoguided equatorial mounts. Slow focal ratios need very very long exposures. (F5 is four times faster than F10 on galaxies and nebulae.) You have a long FL, slow FR scope, which is why I said that it might be worth a full rethink for DS imaging.

What about camera lens imaging of wide views? Here you can do longer exposures because the short focal length will tolerate approximate tracking (which is all you get without an autoguider unless you have a multi thousand pound mount.)

Olly

[sabana]

Thanks. But I'm more confused now. I have seen a plethora of DSI off other users eg clusters, nebulae etc with basic webcams on GEM's with 8 inch refractors. that don't run into many thousands of pounds. Correct me if I am sadly mistaken

[Peter Drew]

Sabana. Can you clarify your posts stating 8" refractor, this could influence the replies.

[sabana]

Its a Celestron Nexstar 8 GOTO.

Sorry for the confusion if any.

[JimStan]

Astro-photography is a science of degrees. By that I mean, you can take a fair picture of many different subjects with fairly simple equipment, but to get the kinds of images that are featured in this forum's "Picture of the Week", requires a lot of time, experience, and money. I doubt that anyone would challenge me on that statement.

I am just beginning astro-photography myself, although I have been an amateur astronomer since before my teenage years. My main camera is a Nikon D-80, with a T mount tied to an 8 inch SCT using an F6.3 adapter. My wide-angle lens is a 500mm F:4 Nikon telephoto ( big chunk of glass ! ) on loan from a very good friend. I have taken some very nice pictures of subjects such as the Pleiades, the "Coathanger", M 42, etc. etc. not to mention several photos of the Moon.

I would not attempt to compare these pictures with those of the experts, but I will say that any one of them shows me FAR MORE about the subject that I am photographing than any amount of time spent viewing these same subjects with the eye and eyepiece !

Besides, seeing what I can pull out of these images is a challenge, and a lot of FUN !

Jim S.

[x6gas]

Ok so your scope is an f/10 SCT not a refractor. That's not ideal for DSO imaging but as Jim says you can have a lot of fun seeing what you can do. Lunar and planetary would be the obvious targets with this set-up though....

[ollypenrice]

Thanks. But I'm more confused now. I have seen a plethora of DSI off other users eg clusters, nebulae etc with basic webcams on GEM's with 8 inch refractors. that don't run into many thousands of pounds. Correct me if I am sadly mistaken

Could you link to these images because I suspect there must be a misunderstanding behind this. To the best of my knowledge no one succeeds in taking images of nebulae in basic webcams and certainly not with webcams in slow f ratio scopes. The small, bright solar system objects are the domain of the webcam and the long focal length, slow f ratio telescope.

A telescope with a long focal length like yours needs three things for long exposures;

1) a camera that can take long exposures, ie a DSLR or cooled CCD.

2) a good equatorial driven mount.

3) an autoguider to correct the inevitable errors in the tracking of that mount. You can get away without the autoguider at the shorter focal lengths of camera lenses etc. By throwing away a lot of exposures you can get maybe a couple of minutes without tracking errors at long focal lengths but even that will not be easy.

The inherent tracking error of a mount at about £1000 is around 20 arcseconds at best. At about four times that you are down to about 5 arcseconds. For 2 arcseconds you are approaching £10,000 as things stand. Few of the pictures you see here are taken on premium mounts. They are taken on sub £1000 mounts fitted with autoguiders which correct their errors in real time. Autoguiding is a topic which will doubtless Google easily.

Olly

[angusb1]

You might want to start off with your camera and one of its lenses on a tripod, or if you don't have one, your alt/az mount, have a read of this first http://stargazerslounge.com/imaging-tips-tricks-techniques/73737-basic-widefield-camera-tripod.html

If you get on ok with it buy a copy of "Making Every Photon Count" by Steve Richards. You need to understand what is in this book if you want to get any results out of imaging. It is a real short cut to understanding what is needed for astrophotograpy. As you say, it isn't impossible to make images using a GEM and your camera without spending a fortune but Olly is quite right when he says that to make really good quality images you need to autoguide using a GEM, and that with a scope of the focal length of yours that is going to cost thousands for a mount.

If you don't have this kind of money (I don't either) you can use your dslr to image DSOs but you will need to do it at a much shorter focal length so use camera lenses. If you have a dslr you probably have some anyway.

Good luck.

[sabana]

Thanks guys. So much to learn, I feel I have just scratched the surface. The autoguider seems a great workaround. And the webcam idea was my mistake for DSO like nebulae. I haven't got the money to invest in higher end cameras. And the every photon book book looks like an interesting read. So now its down to practice practice practice. Thanks.

[yeti monster]

You can make a start by taking widefield single frame images of constellations just by mounting you DSLR on a tripod and aiming at, for example, Ursa Major. A 20 second exposure at ISO 400 and 18mm focal length. A bit of tweekery will bring out faint stars. It isn't HST stuff, but it is rewarding and will give you a good starting point.

I took these on a floating vessel at sea using just such a set up:

And my favourite so far...

Webcamming can be done by manually tracking, although I wouldn't recommend it if you are of a nervous disposition...

[JimStan]

Ok so your scope is an f/10 SCT not a refractor. That's not ideal for DSO imaging but as Jim says you can have a lot of fun seeing what you can do. Lunar and planetary would be the obvious targets with this set-up though....

However, depending on what scope you have, you can possibly obtain a focal-reducer for less money than a premium quality eyepiece.

Celestron ( for sure I know this, because I have one ) makes an F 6.3 "field flattening and coma reducing" lens that screws directly to the back of their SCTs and allows you to screw any and all other eye and camera accessories directly onto the output side of it. This turns your F:10 scope into quite a bit faster F:6.3 scope, capable of photographing many of the smaller DSOs such as galaxies, globular clusters, etc.

BTW, you will want to choose your targets rather carefully for another reason. Any of the nebula that radiate primarily in the IR portion of the spectrum are not going to photograph particularly well , unless you go through the trouble of modifying your camera.

A Nikon probably should be sent away to have this operation done, and Canons as well, especially if you are not a handy-with-your-hands type of person. Canon does sell modified cameras especially for astron-photography use, and you might want to look into that down the line.

BTW Yeti, that third photo is especially nice. I could tell you all about "barn door trackers" but that is a subject for a completely different thread!

Hope this helps.

Jim S.