Large aperture size decision

m11 (Mel) · #1 28-02-2022, 10:43 AM

Hi Everyone,

I have in the planning stage for a large aperture mirror and was looking for advice.

I have narrowed it down to Gordon Waite or Mike Lockwood for my large aperture mirror. I am still not decided which way to go.

I am thinking of around 32" or 34" for either mirror maker and the focal ratio around f/3.5 to f/3.3.

In terms of the mirror looking at Supremax-33 or potentially quartz which comes at a significant cost addition. I am currently thinking quartz might be worth the additional cost being that the mirror will be 2" thick.

In terms of logistics and ease of use I will be sorting out as it is going be a 2 year plus timeframe.

What would everyone's recommendation would be for:

Mirror Maker
Mirror size
Supremax or quartz for that size

Many thanks,

mura_gadi (Steve) · #2 28-02-2022, 11:56 AM

Wow, awesome plans.

Being such a huge mirror, you'd want it to be ready asap not waiting all night...

So, you should be able to work out the acclimation rates between the materials since you have a thickness and size.

The question is then, are your hourly rates of temperature lose great enough to justify the expense of the low expansion material upgrade... (oh and how much deformation you can have and still collimate, which wouldn't be a lot at F3.5)

m11 (Mel) · #3 28-02-2022, 12:19 PM

Haha thanks - Its something I have been thinking about but not sure if I could do it. I think I have saved enough to move this project forward.

Yah - its fair point. I will look at doing the calculations to work out the rate and delta changes.

Its something I haven't worked out but will need to factor in my decision.

I am aware that having a large focal ratio will make the scope taller requiring a larger ladder. Looking to keep it under 3 metres to eyepiece, lower the better I am thinking.

Thanks,

mura_gadi (Steve) · #4 28-02-2022, 02:33 PM

Hi again,

I have seen some of your scopes and posts and your knowledge way way exceeds mine... but...

You could just reverse the viewing use of the proposed monster, use the last 2/3 hours of astro dark and that will eliminate acclimation issues pretty much... Such a scope would deserve the sleep interruption.

Then it's a matter of working out which glass is easier to work with as that will give you the best chance of the best figure.

strongmanmike (Michael) · #5 28-02-2022, 02:51 PM

Having looked through Allans amazing scope at SPSP a few years ago, it feels like if you were to just copy this scope... you would be pretty happy Mel...?

Perhaps he has some valuable input though, have you contacted him?

Mike

m11 (Mel) · #6 28-02-2022, 03:24 PM

Lol I am still learning and its been enlightening process to go through.

Thats a good point and a way to go - working around the mirror and changing the viewing style.

Haha yah - I am hoping to get a dark sky site as the next plan to eliminate some of the issues of a large scope. I still have a bit of time with me I hope.

My reasoning is that quartz if it is available is the way to go - I just need to work the feasibility and whether I am ok to go hard on the scope that would most probably be my last large aperture scope. I can't see myself winning Tattslotto anytime soon to change this.

Quote:

Originally Posted by mura_gadi

Hi again,

I have seen some of your scopes and posts and your knowledge way way exceeds mine... but...

You could just reverse the viewing use of the proposed monster, use the last 2/3 hours of astro dark and that will eliminate acclimation issues pretty much... Such a scope would deserve the sleep interruption.

Then it's a matter of working out which glass is easier to work with as that will give you the best chance of the best figure.

m11 (Mel) · #7 28-02-2022, 03:31 PM

Hey Mike,

You are one lucking guy to be able to view through Allan's 32" SDM scope, so jealous.

I have thought to go the same path but still undecided, I have been mulling over this for awhile. I do like how Gordon does mentoring and teaching but I also like Mike's approach for faster focal ratios and use of quartz.

I did ping Allan recently regarding a bino dob which Allan kindly responded which I was greatly appreciative that he did.

I didn't want to bother Allan again until I felt I was in a position to ask some questions that did his time justice.

Loving how Eagleview is developing - now that is a serious dream come to life.

Quote:

Originally Posted by strongmanmike

Having looked through Allans amazing scope at SPSP a few years ago, it feels like if you were to just copy this scope... you would be pretty happy Mel...?

Perhaps he has some valuable input though, have you contacted him?

Mike