ED80 or Explorer 200p

[SkyExplorer]

Hi,

I'm trying to decide whether to start imaging DSOs with my dslr using my Explorer 200P (f5) or a SW ED80. I have 2 questions I hope I can get answered.

1. What the pros and cons are of using each type of scope for imaging, initially unguided?

2. I live in surrey inside the M25 so the sky here is quiet light polluted, will this have a bearing on what scope I should use to start imaging?

Cheers

[Andrew*]

1. The ED80 has a 600mm focal length, and so is more suited to larger targets, than the 200P with its 1000mm f/l. Use this free program to get an idea of what the two scopes will fit in the FOV. The focal length also indicates how long your exposure times can be before you get star trailing due to mount error. The shorter focal length can be used for longer trail-free exposures.

The ED80's longer focal ratio of f/7.5 means it will require double the exposure time to get the same amount of detail as the f/5 200p.

The 200P requires a coma corrector to avoid the comet-shaped stars in the corner of the FOV.

2. It doesn't really make too much difference in terms of which scope to use, but do consider a light pollution rejection filter.

HTH

Andrew

[Andrew*]

Another point worth mentioning is that your mount will be more comfortable under the ED80 as it's lighter and shorter.

All things weighed up, I think you should try with the ED80. You will find it easier and you will get better results. It will require longer focal lengths, but it's better optically corrected than an un-corrected newtonian, and the wider FOV is easier to manage.

With a coma corrector, your choice of scope will mainly depend on the particular target you wish to image.

Andrew

[Andrew*]

Another point worth mentioning is that your mount will be more comfortable under the ED80 as it's lighter and shorter.

All things weighed up, I think you should try with the ED80. You will find it easier and you will get better results. It will require longer focal lengths, but it's better optically corrected than an un-corrected newtonian, and the wider FOV is easier to manage.

With a coma corrector on the newt, your choice of scope will mainly depend on the particular target you wish to image.

Andrew

[SkyExplorer]

So light pollution has no real bearing the performance of both scope if a light polution filter is applied?

I guess the ED80 would be easier to manage (less bulky)

your choice of scope will mainly depend on the particular target you wish to image

Could you please explain a bit more about this??

Thanks

[Andrew*]

LP will affect BOTH scopes, but to about the same degree. At least this is how far my understanding goes. An LP filter will not fix LP altogether, merely help!

Regarding the scope for target question - as I said it's to do with the size of target due to the difference in focal length. The longer focal length will better frame a smaller object and vice versa. Saying that, the 200P gets in the main Pleiades stars all at once, so it's not exactly a small FOV either.

Andrew

[steppenwolf]

To start with, I would recommend the ED80 for the following reasons:-

1. The shorter focal length will be less demanding in terms of tracking accuracy

2. As Andrew has suggested, many Deep Sky Objects are large and the shorter focal length will give you a wider field of view making it easier to frame and encompass these larger objects

3. The lighter ED80 will be easier to set up and will be less work for your mount

4. You will find it easier to attach your camera and obtain focus (some Newtonian Reflectors have great difficulty obtaining focus with a camera because they have a small amount of inwards focus travel - this is dependent on the type of focus assembly on your mount)

5. As Andrew has said, coma will be a problem with the Reflector - this is fixable but you could have all sorts of problems with obtaining focus again

Once your experience has advanced, you can move up to using the longer focal length reflector and be better placed to resolving the potential problems of tracking, focus and coma.

[Andrew*]

It will require longer focal lengths,

Excuse me - make that "longer exposure times"!

[SkyExplorer]

Thanks guys for the update.

When you say longer focal length of the newt (1000mm) compared to 650mm of ED80 does that take into account the speed of the scope. The newt is f5 and the ED80 is f7.5 - Sorry for the simple question.

Cheers

Steve

[Andrew*]

They're all connected. Focal ratio is the focal length divided by the aperture, so:

ED80 - 600/80 = f/7.5

200P - 1000/200 = f/5

So the 200P has a longer f/l, but is faster (lower f/) due to having a much larger aperture.

HTH

Andrew

[SkyExplorer]

1. The shorter focal length will be less demanding in terms of tracking accuracy

2. As Andrew has suggested, many Deep Sky Objects are large and the shorter focal length will give you a wider field of view making it easier to frame and encompass these larger objects

So the shorter focal length of the ED80 as stated will mean a wider fov however it may need longer exposures due it being a slower scope than the f5 newt so it lets in less light?

Sorry for the relatively simple questions.

Steve

[steppenwolf]

So the shorter focal length of the ED80 as stated will mean a wider fov however it may need longer exposures due it being a slower scope than the f5 newt so it lets in less light?

That's corect.

[SkyExplorer]

Just read this off steppenwolf's site "Light Pollution - the greater the light pollution, the shorter the exposures you can take before the image becomes ‘fogged’."

Is this something I should be concerned about regarding the ED80 vs 8" newt I have?

[Andrew*]

Yes, both. But this only becomes a problem with exposures over say 2 minutes, which requires guiding.

[SkyExplorer]

ah okay, so getting started in imaging I should not worry too much about this.

Does the book "Every photon count" cover all of this? Do you think it worth while for me to buy it?

Thanks again Andrew

Steve

[steppenwolf]

Does the book "Every photon count" cover all of this? Do you think it worth while for me to buy it?

I can't possibly answer that one for obvious reasons

[Catanonia]

lol that would be a yes

[SkyExplorer]

I can't possibly answer that one for obvious reasons

LOL !!!

So I guess what I am hearing is that the ED80 would be an easier scope to start imaging with.

[steppenwolf]

So I guess what I am hearing is that the ED80 would be an easier scope to start imaging with.

IMHO, yes but both make good imaging platforms if you can resolve the focussing issues on the Reflector.

[SkyExplorer]

I've already managed to take images of the moon with my 450d attached to the Explorer 200p using a T-ring adaptor, so focusing has not proved an issue with it.