New scope choice

[souls33k3r]

Hi all,

I don't know what's wrong with me but I just can't make up my mind on a new wide field scope. 

I basically want something with R&P focuser (to avoid slippage when using ASI1600MM-COOL camera and the ZWO FW), short focal length (350 - 400 after reducer) and something that is fast (F/5 or under) 

I don't want to over spend if I can help it but then I initially budgeted myself for anything under £800 for a scope and then adding a FF/FR for another £200. If I have to buy something that has a built in FF and with short focal length and that is fast,  that brings me to £1300 range... Ouch

Choosing between the different refractors has been nothing but hair pulling moment for me. 

Should I buy something with a built in Field Flattener or something without? What are the pros and cons of both? 

 scope suggestions/recommendations?  (should be a refractor) 

Also whatever I buy, I'll keep it till it breaks and just maybe this will be my last purchase for the foreseeable future so want to make the correct decision. 

Thanks in advance

 

[ollypenrice]

It's easier to go for a natural flatfield like a Petzval in that you don't need to respect a chip distance, but if you are going to keep the rig for a long time then the minor faff of setting up the right chip distance behind a reducer will soon be forgotten.

Personally I think the biggest issue at the moment is quality control. There are plenty of good little imaging refractors out there provided you get a good one. So I think your choice of retailer might be more important than your choice of scope... We all know who has an excellent returns policy. ^^^ 

Olly

 

[souls33k3r]

13 hours ago, ollypenrice said:

It's easier to go for a natural flatfield like a Petzval in that you don't need to respect a chip distance, but if you are going to keep the rig for a long time then the minor faff of setting up the right chip distance behind a reducer will soon be forgotten.

Personally I think the biggest issue at the moment is quality control. There are plenty of good little imaging refractors out there provided you get a good one. So I think your choice of retailer might be more important than your choice of scope... We all know who has an excellent returns policy. ^^^ 

Olly

 

Many thanks for taking time to reply. I agree with the fact that quality control is the biggest issue at the moment but then you spend so much money on a piece of kit and you're being the test subject to figure out all the issues is just not fair. Plus there aren't enough clear nights in a year to mess about figuring certain issues. The check and tune aspect of it is good but so far limited to only a handful of scope from what i can see.

Not sure what good scopes are out there which will potentially be CA free and also to tag along a FF/FR will give basically flat field?

Orion ED80T was on my list but i've heard so many bad reviews of it's focuser and people then changing it to moonlite which adds more money to it. So basically i'm looking for a good scope without any of these issues.

[ollypenrice]

33 minutes ago, souls33k3r said:

Many thanks for taking time to reply. I agree with the fact that quality control is the biggest issue at the moment but then you spend so much money on a piece of kit and you're being the test subject to figure out all the issues is just not fair. Plus there aren't enough clear nights in a year to mess about figuring certain issues. The check and tune aspect of it is good but so far limited to only a handful of scope from what i can see.

Not sure what good scopes are out there which will potentially be CA free and also to tag along a FF/FR will give basically flat field?

Orion ED80T was on my list but i've heard so many bad reviews of it's focuser and people then changing it to moonlite which adds more money to it. So basically i'm looking for a good scope without any of these issues.

I wouldn't buy a Moonlite for imaging. I don't think much of the one I have. The roller drives smooth anodized aluminium.

This https://www.firstlightoptics.com/william-optics/william-optics-star-71-ii-4-element-refractor.html has a rack and pinion. Much to be preferred, in my view, over any Crayford.

Olly

 

[gnomus]

I have a Williams Optics Star 71.  In fact, I have two.  The First iteration of this (5 element) was plagued with QC issues.  I had three in all to get one good one.  The Mark II I got was good first time, but who knows if they all are.  

If I was starting afresh, I would be tempted by the Esprit 80.  But (unlike the 100 and the 120) it does not use the usual scope rings, and it is not at all clear to me how you are supposed to attach a decent guide scope.  This is a triplet so you would need the field flattener.

There are clones of the WO 71, but I agree with Olly - choice of retailer is crucially important.  I have found FLO to be a very safe way of buying this stuff.  Others have been ... ... difficult (I remembered to take my diplomacy pill this morning).

[souls33k3r]

apart from the Williams Optics Star 71 scope (which is the one i mentioned being at £1300), what other scope choices that i do have that are reliable with all these aspects mentioned above?

[ronin]

Suspect you are looking at the overseas options then.

There is the StellarVue 70mm triplet, but at $1000 and shipping and VAT means it will come out at on the £1000 mark. Does have a 2.5" R+P focuser. But there would still be the question of the flattener I suppose. So likely back to the £1300 mark I suspect still.

There is as mentioned previously the new GT71 from WO, bit less at £960 still likely to come in at around tht in £ however. Although from a problem I am having check out the Astro Tech site. They have a 72mm triplet F/6, FPL-53 which on the Astronomics site is priced at $470, 2" R&P focuser. Maybe ask on the CN site about these scopes in general.

Not sure if either make is easily available in the UK or EU.

Cannot make much sense of the PrimaLuce items.

Not sure about the ones with the built in flatteners as they seemed a good idea but never caught on and that tends to make me think that there is a fundimental complication with them that made people look at other and possibly more simple designs.

Could try the TS/APM offerings but they seem a case of some good, some poor, so again inconsistancy.

Having just looked a TV 76 is out of range.

 

[Andyb90]

How about this:

I can see the last poster has sent a pm but it's not listed as sold. Seems like a good deal. 

Andy.

[souls33k3r]

Shame i missed out on the above deal.

Ronin, very good points raised. I can get the scope over without any issues (can ask mates to bring one over when they're flying) but what happens if i have to get the scope looked at under warranty, getting it back will certainly poise much troubles.

Primulace scopes look good though, maybe it's a new thing for them so not taking off like they should. Plus the price bracket they're advertising their scopes, you can get the same thing from another supplier with a tested reputation.

Question to all though, i'm wondering, the quad scopes make so much sense on paper with fixed FL and f ratio and no faffing about with finding spacers and correct FF/FR, then why haven't these taken off? why would someone prefer a say 80/480 scope only to reduce it to the same FL as a quad and more or less the same f ratio?

[ronin]

The Primaluce scopes appear to be clones/copies of older William Optics scopes, their 90 Airy is a Megrez 90, as are others they offer. I suppose they made some agreement with WO as even the bodies and fittings are very, very similar. Almost a case of WO no longer produce but if you want one then go to the Primaluce site.

Like you I have no idea why the built in flattener scopes never made an impression. APM had one at the time WO brought out the GTF range. Equally WO have a habit of not making a serious release of scopes in the UK or EU so likely very few are in use here. Seem to recall the GTF-102 was a popular one in the US.

Could find that part of it was tht imagers want faster and faster scopes and the WO GTF's when the bits were all in place the result was a slightly slower scope then the standard GT-81/102. I think the idea of a "slower" imaging scope made people/imagers reconsider.

Another thing that crossed the empty space between my ears was that to an extent for better then the usual items you are going to have to increase the budget significantly. LZOS lens are good but much higher budget, same for Astro Physics and even a used TMB 92 is likely around twice the budget - if you can locate one. TV's are always reported a good but 3x your budget. There is not a bit better offering at not too great a cost increase.

The one I wanted looks like I will have to forget. A strange situation has occurred where I just seemingly cannot make the purchase. Slightly crazy impasse.

[souls33k3r]

While i was sitting for a few upgrades of the servers, i was thinking and doing some crude calculations (like you do) as the difference between a f/6.5 vs a f/4.9 scope (ignoring the FOV) and the calculations are as below, feel free to comment if you guys want.

I am taking under consideration that using the CMOS chip, you can go for more exposures with less exposure time

- Difference between a f/6.5 vs f/4.9 scope is 1.6 which means for a 300s exposure on a f/6.5 scope, you'll only need 252s on a f/4.9 scope or for 180s exposure on a f/6.5, you'll only need 151.2s on f/4.9 scope to get the same amount of data.

- Assuming you do 50 exposures using 180s exposure on f/6.5 scope, you get around 150min of exposures and getting the same data on a f/4.9 scope using using 50 exposures but at 151.2s you get 126min which is only just saving 24min. Now consider taking all three NB filters for example, that is a saving of 1hr and 12min.

Two questions to ask here are whether the airy disk will matter to most people or not? and also the extra £500 just to save 1hr and 12min? is it work it?

Decisions, decisions ... this is not an easy hobby 

 

 

 

 

[Alien 13]

Not sure if your initial calculation is correct, a 300 s exposure on a f/6.5 scope should be 167s with a scope of f/4.9.

Alan

[souls33k3r]

3 minutes ago, Alien 13 said:

Not sure if your initial calculation is correct, a 300 s exposure on a f/6.5 scope should be 167s with a scope of f/4.9.

Alan

Hi Alan, i may very well be wrong but would you help me understand how you came to 167s on a f/4.9 please?

[Alien 13]

2 minutes ago, souls33k3r said:

Hi Alan, i may very well be wrong but would you help me understand how you came to 167s on a f/4.9 please?

I used this calculator https://rechneronline.de/exposure/ I used the initial numbers you gave for the f/6.5 to get a value for EV then kept that and changed the f ratio to f/4.9 and ask it to calc a new exposure time.

Alan

[souls33k3r]

21 minutes ago, Alien 13 said:

I used this calculator https://rechneronline.de/exposure/ I used the initial numbers you gave for the f/6.5 to get a value for EV then kept that and changed the f ratio to f/4.9 and ask it to calc a new exposure time.

Alan

unfortunately i'm still none the wiser

Different settings giving different values there. Wish there was a comparison chart of some sort.

I understand a f/4.9 will be faster but how much faster when compared to say a f/6.5 scope ... of course it looks like it will be 1.6x but what doesn't that mean that 300/1.6 will be 187s ? that's how i'm seeing it now come to think of it rather than 167s

 

[Alien 13]

4 minutes ago, souls33k3r said:

unfortunately i'm still none the wiser

Different settings giving different values there. Wish there was a comparison chart of some sort.

 

I think the calculator is aimed at DSLRs but it looks like it gives reasonable comparison values, I did look at a few charts but they seem to only give the std f ratio numbers.

Alan

[Andyb90]

On 2017-7-10 at 13:19, gnomus said:

If I was starting afresh, I would be tempted by the Esprit 80.  But (unlike the 100 and the 120) it does not use the usual scope rings, and it is not at all clear to me how you are supposed to attach a decent guide scope.  This is a triplet so you would need the field flattener.

I also looked at the Esprit 80 a while back. The mounting foot on the bottom of the OTA can be removed, so in theory it could be put in tube rings, but there isn't much space between the fixed dew shield and the focuser to place the rings. Also if you wanted to put a dew heater tape at the back of the dew shield there would be even less room. 

Andy.

[alexbb]

If I had the money to spend, I would go for an Esprit 80. This is actually in my plans, sooner or later. Where I live, I didn't need until now a dew heater and I have the guide scope set on the side, not on top.

I don't think you can go wrong neither with the esprit, neither with the wo st 71 ii.