Aperture fever visualised

[Radman40]

We often see discussions and questions on SGL about the importance of the size of the telescope aperture/objective in terms of its light gathering ability so I thought I would have a go a taking some images to illustrate the discussions. The larger the aperture the brighter faint objects (like galaxies) will appear at the eyepiece. The other thing to consider is resolution or the ability to see fine detail on the moon and planets or within star clusters. Basically the bigger your telescope objective get the more detail you get (within the limits of what the atmosphere will allow us to see). Here are two images of a feature on the moon, one taken with an 80mm objective and one with a 250mm objective. I tired to keep all the image acquisition and processing factors as similar as possible (ish). If you are starting out in visual observing then the advice is often given is to go for a 8 inch (200mm) dobsonian telescope. I hope these images will show you why this is good advice.

80 mm.tif

250mm.tif

[faulksy]

thats good, didnt see much difference in the second image but the moon was loads better. thanks for that

[Laurie61]

Hi Radman, it's an interesting comparison. I have made a rough gif of your two images, you can certainly see a difference hope this works..

[John]

I think what aperture gives you is the potential of higher levels of performance. There are a number of factors including seeing conditions (major factor), state of collimation / cooling of scope, eyepiece quality and observer experience that determine what you actually see on a specific occasion though and these are somewhat difficult to simulate being extremely variable. A guide to the potential differences is useful as long as folks understand why their scope might not always achieve that or may even sometimes exceed it.

[Radman40]

Yes, it works really well! Many thanks for taking the time to do this Laurie.

[SnakeyJ]

There's quite a nice comparison on the obsession website, though it should come with a wealth warning

[Radman40]

All relevant points John. Thanks for adding these. As an addendum the images were taken under very average seeing conditions. I got up early when the moon was high in the sky and about to transit, collimated the scope, cooled them for several hours but the seeing was not that good...some things you can control and some things you cant. Perhaps I should do a couple of images where other variables are changed to see what difference that makes e.g. cooling and collimation. I can feel a project coming on.

[Laurie61]

Damian Peach produced a nice simulation of different aperture scopes on his site- http://www.damianpeach.com/simulation.htm

A simulation allows things like collimation, optical quality and seeing to be standardised so just the aperture difference is seen. I would say they show a similar optical improvement, 10cm-25cm, as the images above. Wish I could take Saturn shots like that