Jupiter Scale

[Charic]

A request please?  Does anyone have two images of Jupiter, one taken through their 8" reflector,  and those lucky enough to own two scopes, or access  to a 12"  the same image through the 12" reflector.

I'm looking for a photographic  comparison to compare the image scale.

Thanks in advance.

[Ruud]

Hi Charic, I don't have such images, but it's focal length that determines the image scale, not aperture.

[Charic]

......yes, that's correct, although I never  meant it to sound as if the aperture was to blame, I had to mention  8" and 12" as this is the scope I want to compare?  the 300P  has a 1500mm focal length as opposed to the 1200mm  on the 8" scope. 

Its going to be difficult for me to obtain  a side-by-side comparison between these scopes , so hopefully a photo can show me visually if there is a reasonable increase, and determine if I need to go to a 12" scope

But thanks anyway.

[Freddie]

Why not use one of the field of view calculators to show what you want? Here's a link to one

http://www.12dstring.me.uk/fov.htm

[Ruud]

Ah, of course. And when you consider that people often use barlows etcetera to bring the focal ratio to an optimal value, then aperture comes back in the picture too.

[John]

If you use the same eyepiece in both scopes, the apparent size of Jupiter would be 25% larger with the 300P due to the longer focal length. You might see a little more detail or the detail that is there a little more easily with the larger aperture but the seeing conditions will determine the extent of that of course.

[Charic]

Why not use one of the field of view calculators to show what you want? Here's a link to one

http://www.12dstring.me.uk/fov.htm

That works......cheers!

There's not as much difference as I thought there might be?  And I know its only a simulator!

[John]

That works......cheers!

There's not as much difference as I thought there might be?  And I know its only a simulator!

With an F/4 12" the image scale would be just the same as with your 200P (assuming the same eyepiece is used) but there should be more contrast and resolution available within that image with the larger aperture.

[Charic]

Using that simulator, I don't think I require the 12".  Although I have seen that link before, I have never truly set it up properly, but have done tonight  and  the difference is not  so alarming?

For the same price of the scope, I could  now purchase the three Delos Eps that I wish to trial?  I know the sim cannot show with optical clarity,  the difference between my EPs  with regards to a Meade 4000 or BST,  or my TV Plossls , and would my old eyes see any real  benefit with these fine optics over my BSts, apart from the extra 12° afov ?

Maybe I should continue  until the Winter has passed with what I already own,  to better asses, if the need is required, or am I just spending for the sake of it?  Funding is not the issue,  and to better test my system,  go to the darkest sites I know, with tent, Thermos,  and a cooker? The darkest sites I know,  could soon be covered with snow? You just cant win!

[John]

The move from 8" to 12" would give you more of a performance increase than a move from BST Explorers to Delos eyepieces I reckon. An eyepiece can only present the information (light) that the scope has gathered. With a 4" larger aperture you have a lot more information.

A 12" dob is a lot larger and more clumbersome than an 8" though. It's not a decision to be take lightly I agree.

[Charic]

Cheers John, that all makes sense. 

Just playing with some ideas, that have been brewing for a while, and  the opportunity to buy something now before my new car  arrives ?  ( will have to drop the trim levels!)

And yes, it was the performance increase in the overall scope that was top of my feature list.  perhaps I should go even bigger, 16" ( wake up charic!) 

I was hoping to observe tonight, a first for many Months, but who puts my Dob tent in the attic (  three hours of searching? )

I have one more week before a well earned break, so have all the time in the World to carry out some tests, unless I overdo the work load with some more shed building?

Thanks everyone for the replies. 

[callisto]

Why not use one of the field of view calculators to show what you want? Here's a link to one

http://www.12dstring.me.uk/fov.htm

Great tool, thanks for posting 

[John]

Cheers John, that all makes sense. 

Just playing with some ideas, that have been brewing for a while, and  the opportunity to buy something now before my new car  arrives ?  ( will have to drop the trim levels!)

And yes, it was the performance increase in the overall scope that was top of my feature list.  perhaps I should go even bigger, 16" ( wake up charic!) 

I was hoping to observe tonight, a first for many Months, but who puts my Dob tent in the attic (  three hours of searching? )

I have one more week before a well earned break, so have all the time in the World to carry out some tests, unless I overdo the work load with some more shed building?

Thanks everyone for the replies. 

16" - 18" would be my next step but, having seen them and used them, I know it's just not a practical proposition given my observing site and scope storage constraints

It's still nice to think through the possibilites from time to time though

[Moonshane]

My 12"f4 is less cumbersome than my schools 8"f6 mainly due to design. I'd mot make an aperture increase decision based on planetary expectation. The differences are less than for faint objects. I'd much sooner have my 12"f4 than a 8"f6 for all objects.