Zooming in without a lens

[planecrazzzy]

My question is this... When the camera is mounted on the telescope...
There are no lenses or Barlow ... So how do you zoom in ?
I'm saving up for a Cooled , Mono , Color wheel and maybe auto focus.
Probably close to $2500 bucks.

But I've wondered just how does it work.... Is it done through the computer ?

Gotta Fly...

[OzEclipse]

The focal length of most telescopes are fixed, no zoom, just focus. You can crop the image so it looks bigger relative to the frame but you are not zooming in. You are cropping.

You can increase the focal length of a compound telescope like an SCT or Mak by shortening the distance between the two mirrors and shifting the camera backwards.

Joe

[KathyNS]

The telescope IS the lens.

For my DSLR, I have several non-zoom lenses: a 28mm Pentax, a 50mm Pentax, an 800mm Orion, a 1000mm Celestron, a 2000mm Celestron, and a 2800mm Celestron. The first two were designed to be camera lenses. The last four were designed as telescopes. Some are refractors, some are catadioptric. They all work the same way. The image scale / field of view is determined by the focal length.

[planecrazzzy]

OK...I see it is a crop process....focal has more to do with focus...

Thanks

[Gfamily]

A rule of thumb is that diagonal across the sensor gives you an idea of what an eyepiece would see.
So if you were using a full frame 35mm camera, the image would be similar to what you'd see through a 35mm eyepiece.
A smaller sensor would give you something like a shorter focal length eyepiece.

[OzEclipse]

A rule of thumb is that diagonal across the sensor gives you an idea of what an eyepiece would see.
So if you were using a full frame 35mm camera, the image would be similar to what you'd see through a 35mm eyepiece.
A smaller sensor would give you something like a shorter focal length eyepiece.

Various eyepiece designs can have widely different apparent fields of view [AFOV] varying from 40 to 100 degrees so this rule of thumb doesn't really make sense.

The visual magnification M is
M = [Telescope Focal Length] ÷ [Eyepiece Focal Length]

The True Field of View TFOV is
TFOV =AFOV ÷ M

The photographic field of view PFOV of a telescope is easily calculated

PFOV = 57.3 x [Sensor Dimension] ÷ [Telescope Focal Length]

Always use the same units for measurements in the formulae eg focal length in mm, sensor size in mm.

For example, with a 1000mm focal length, an APSc sensor diagonal has a 1.6 degree field while a full frame has a 2.35 degree field. A 31mm Nagler, one of the widest field eyepieces has a 2.5 degree field of view but an average 30mm Plossl will only have a 1.6 degree field. Easiest thing is to just do the calculations to work out true angle of view.

Joe

[Gfamily]

Sigh, that's why it's called a rule of thumb.

It gives you a starting point.

Obviously, different EP designs have different Fovs, but if you've got a beginner asking 'what does this mean?' it's a starting point.

[planecrazzzy]

https://www.highpointscientific.com/zwo ... asi533mm-p

This is something I was thinking about... with a electronic filter wheel...

[Graeme1858]

https://www.highpointscientific.com/zwo ... asi533mm-p

This is something I was thinking about... with a electronic filter wheel...

This is how you would see the Moon with that camera using different telescopes with focal lengths of 660mm 1000mm 2800mm.

You can put your actual telescope into the First Light Optics Astronomy Tools.

Graeme

[JayTee]

I don't mean to dampen your spirit, and what I'm about to tell you can be disregarded, but with your limited experience starting with a mono camera and filter wheel is like being put in the middle of a whirlpool in the middle of the Pacific Ocean when you don't know how to swim. Can you survive, maybe, will it be fun, probably not. There are easier routes to start your AP journey.

Cheers,

[planecrazzzy]

I don't mean to dampen your spirit, and what I'm about to tell you can be disregarded, but with your limited experience starting with a mono camera and filter wheel is like being put in the middle of a whirlpool in the middle of the Pacific Ocean when you don't know how to swim. Can you survive, maybe, will it be fun, probably not. There are easier routes to start your AP journey.

Cheers,

I probably need to find a club to get a better idea about it.... So far it's online searching...

[Graeme1858]

I probably need to find a club to get a better idea about it.... So far it's online searching...

Most of us started with a visual set up. A lot of the complications of astrophotography are easier if you are already familiar and proficient using your telescope.

Then when you move into astrophotography most would recommend starting with a colour camera, either a DSLR or a dedicated astro camera.

There is an excellent colour version of the camera you listed:

https://www.highpointscientific.com/zwo ... asi533mc-p

The ASI533 has a square sensor and so produces a square image rather than the usual rectangular. There's a few here that use one.

Have you got, or got your eye on any particular telescope yet?

Graeme

[planecrazzzy]

Couple things... One... I'm told the Camera needs to be cooled... The cheaper ones aren't...
The other was Mono gives better results... So that's why I choose a filter wheel... auto or not...
Spending alot of money on these ? yes... but skipping the cost of the cheaper stuff to get to this...
In the long run , that's saving money....
Basically it's learning the computer...
My Telescopes guiding and tracking are in place... Just add camera

Cooled
Mono
Filters

So with THOSE three .... What's the suggestions ?.... Anything else I don't want to hear.

[planecrazzzy]

.
https://telescopes.net/zwo-asi1600mm-co ... undle.html
.
This is what I really want.... the 1600.... So I thought I WAS starting slow .... By the time I save the money...
I probably WILL buy this one
I don't know why anyone would say not to...
.
Yes.... it will take some learning.... That's what I'm here for.
.
Gotta Fly...
.

[Graeme1858]

That's the camera and filter set I'm using.

Will you be using a separate guide telescope or an off axis guider?

Graeme