Lunt 35 v Coronado PST Shootout

[NGC 1502]

The following is a comparison review between my own Lunt LS35T H-alpha, ( basic model with B400 blocking filter ) and a Coronado PST H-alpha, the property of my local astronomy club.

Please remember that the following is one persons opinion, and that mass production can lead to differences between individual instruments. For brevity, I will refer to them as the Lunt and the PST. The Lunt is a 35mm < 0.75 Angstrom unit, the PST is 40mm < 1.0 Angstrom. I expected the Lunt < 0.75 A. would give better disc detail, then realised that expectations can lead to bias, not a good thing to bring to a comparison review !! I have tried hard to give an accurate idea of how these instruments compare.

The Lunt comes with two tube rings and an adaptor to fit a standard photo tripod, whilst the PST has a threaded hole to achieve the same. If mounted this way, unless the tripod is a heavy duty model, it makes Solar viewing a wobbly hit & miss experience. I think it is far better to mount them on something more substantial with slow motion controls. The Lunt's tube rings were stored in a separate compartment within the box. I altered the foam within the box to allow the tube rings to be left on the scope for a faster setup, and fitted a short dovetail for attaching to my alt-az mount. I padded the tube with plastic strip to avoid the guide scope type screws from marring the paint. (The screws are plastic tipped). The Lunt has a helical focuser, the PST has a chrome screw, both are fine by me. The Lunt has a refractor style blocking filter, I find this is handy for rotating the eyepiece to a comfortable position. The PST eyepiece port is fixed.

The important thing of course, is how do the views through these entry-level scopes compare ? With them both set up next to each other on their own alt-az mounts with slow motion controls, and with blue transparent skies, I was keen to find out !!

Both instruments have a 400mm focal length which makes comparison easier, as a given eyepiece produces the same magnification. I used six eyepieces from 40mm through to 7mm, carefully focusing and using the tuning controls, with multiple views at each magnification, and making notes, before coming to a conclusion.

I found that at every magnification the Lunt gave brighter views. Viewing prominences, I could discern no visible difference between the scopes at any magnification from 10x to 57x. Both gave very satisfying views. With disc detail, under these excellent conditions, a lot of intricate structure was visible in both, however, there was a very slight increase in contrast, with the PST just a winner here, by a whisker. But it took many views, adjusting focus & tuner, and at different magnifications, to make this call. The Lunt's 0.75 A. did not put it ahead. (told you I wasn't biased )

The contest is not over yet however ! There is another issue, the "sweet spot", that is the area of good definition within the visible field of view. The clear winner here is the Lunt. My favourite eyepiece with both scopes is a 14mm giving 29x and I placed a prominence just within the sweet spot. I then timed how long it took to drift across the sweet spot. With the Lunt, I got 1min 55secs before I needed to adjust the slow motion controls, the PST gave just 45secs. I did multiple timings to be sure. Now, each of these scopes is worth having, but which is best ?

You need to weigh up the following :- The PST has a very very slight edge on disc detail contrast, the Lunt has a much larger sweet spot. If you are using a driven mount then the sweet spot is less of an issue.

One insignificant difference is the orientation of the field of view. If a prominence is at 11 o'clock on the limb in the Lunt, then it will be at 7 o'clock in the PST.

If you want significantly better views, then you will need to spend a lot more money. Or you could just get some Baader film or similar, and content yourself with viewing Sunspots with any small scope you may already have. Happy viewing and clear days as well as nights from Ed.

Update :

The excellent viewing conditions of the 22nd May have continued for the 23rd & 24th, so I took advantage of this, while I still have the PST on loan, for further comparisons. The PST definitely has the edge ( just ) for viewing disc detail. But under these very favourable conditions, both scopes showed an intricate mass of subtle solar features. Just remember to not over magnify, focus & tune carefully, and keep the chosen area within the sweet spot. This latter is much more critical with the PST. I think that 40x is max with both instruments for good sharp views of prominences, less for disc detail, around 24x to 30x I think. Either scope is a good entry into H-alpha viewing. I'm afraid I can't comment on how these two compare for imaging. Best regards to all, Ed.

Edited May 24, 2010 by NGC 1502

[A McEwan]

Interesting comparison. I'm surprised at the PST giving better disc detail, but not at all surprised by the Sweet Spot comparison. Amazing what you can get for your money these days for H-alpha viewing. Congrats on the new scope - hope you continue to enjoy using it!

Ant

[Peter Drew]

A deal breaker for me would be whether the Lunt could be modded in the same way as the PST can be, leading to much better performance at reasonable cost than either of the original configurations.

[MrJulius]

Nice comparison Ed, could you please add some spaces so it will be easier to read.

[brianb]

A deal breaker for me would be whether the Lunt could be modded in the same way as the PST can be, leading to much better performance at reasonable cost than either of the original configurations.

There are downsides to the modification - the increased aperture PST is not suitable for wide area views due to the "sweet spot".

The LS35 has not been around long enough for anyone to seriously consider hacking it. But I'd respectfully suggest that it might be better to stick to what is known, if that's really what you want to do.

[NGC 1502]

Post #4, Sorry about that, I've just added a few spaces !! I was trying to save paper Ed.

Edited May 24, 2010 by NGC 1502

[ollypenrice]

Very good review. A guest was here recently with a double stacked Lundt 60 and I was blown away by seeing prominences so easily on the disc itself, let alone on the limb.

Olly

[brianb]

seeing prominences so easily on the disc itself

When they're called "filaments". There have been a lot of notable ones recently.

[Solar B]

A very good and Honest review indeed,for me its a case of Lunt does it again im afraid,making wild bandwidth claims about their

instruments that cannot be substantiated.

Brian

[johninderby]

Now let me see........ They're both low cost entry level Ha scopes and the Lunt 35 and PST are about tied in overall performance, despite the PST having 14% more aperture, and the Lunt costs less than the PST. The biggest headache with the PST is that dammed small "sweet spot" which means that you can only see a small part of the surface in any detail at any one time. That's the reason I got rid of my PST.

John

[GazOC]

A deal breaker for me would be whether the Lunt could be modded in the same way as the PST can be, leading to much better performance at reasonable cost than either of the original configurations.

Same here.

[Solar B]

In all honesty the LS35 should walk all over a PST,due to the fact it uses a 35mm "front" mount etalon (same one that is "rear" mounted in the LS60) so employs a much larger clear aperture etalon than the also "rear" mounted PST etalon which is 20-22mm i think .

I think the stage 2, PST mods are very good but only really from

an imaging perspective as you are constrained to the PST etalons

bandwidth and size so no matter how large your aperture is, say 200mm it will only ever be a 200mm PST,would like a look through one that large though .

Brian

[Peter Drew]

I managed to obtain a 145mm diameter ERF so I can "stretch" my PST to that aperture. Although it is true that the bandwidth of the etalon remains as standard, the extra scope aperture pays dividends in respect of resolution during good seeing and will stand higher magnification. At the end of the day it depends on what type of image you prefer, my preference is for the bright prominence performance from a .7 etalon as opposed to the darker disc performance of a double stacked unit. I'm happy with the enhanced PST type performance as a result of the "mod".

[Solar B]

Well im glad your happy with your Mod Peter and that certainly is a stretch 145mm into a 22mm etalon

I think you would find that Proms are better viewed nearer 1.0A though.Some suggest their PST etalons are around 0.7A which would be an outstanding performance from a 300 quid etalon,i think in reality they may not be.

Talking about squeezing aperture from small etalons the LS152 only uses a 60mm etalon.

Brian

Edited May 24, 2010 by Solar B

[brianb]

Some suggest their PST etalons are around 0.7A which would be an outstanding performance from a 300 quid etalon,i think in reality they may not be.

The PST etalons are made to a specification - if they turn out a bit better than the design spec, they're not going to junk them, and there is no other market.

The way the thing is constructed gives a theoretical bandwidth of 0.65A. In practice the f/10 cone broadens than to ~0.75A. If made perfectly (not all will be!) The "pass unit" criterion is 1.0A.

0.7A bandpass is not an issue for viewing prominences, but it does make the tuning a bit more critical.

[Solar B]

Mr M Ludes had suggested a couple of years ago that it Would be possible to make a single 0.5A filter with reference to Mr A Lunt,

so naturally it is possible to make low bandwidth filters but at

a cost.

I have owned and tried numerous PSTs but i feel that the differences in contrast some exhibited had as much to do with the

light path as their etalons EG old V new design and other

small permutations in manufacture such as coatings.

PS there is only one person that i would go to,to guarantee a filters bandwidth and we both know who that is.

Edited May 24, 2010 by Solar B

[simon955]

Thanks for the detailed review, I am looking for a startup solarscope, still undecided tho.

[Merlin66]

OT but when the PST's are modded, the 20mm etalon acts as an aperture stop. So the "final effective aperture" is dependent on the focal length/ focal ratio of the "donor" scope. Also the end result is ALWAYS an f10 beam. The sweet spot does vary with the donor scope parameters.

I'm collecting data on the image size of the sun in known pixel dimensions to verify this. So far none of the data refutes the f10 answer. So a 180mm aperture donor may only end up 93mm "effective" depending on the various parameters.

Ken

[Peter Drew]

Much as I should have known better, I twigged only recently, that as Ken says, a donor telescope faster than F10 may well have the objective vignetted by the 20mm etalon aperture of the PST. Based on this, I now calculate that the 80mm ERF on my Sky 90 mod is providing a clear aperture of only around 53mm which belies the outstanding performance it gives. I do know someone who has a 90mm and 60mm coronado and claims that on average days the 60mm is preferable to the 90 so this might be a factor.

[NickH]

Side by side comparison of a PST80 and the SV50 which is a measured 0.7A instrument, and the views are identical..(in terms of surface detail visible though caveat for the sweet spot on full disc) At F25-F40, the PST80 absolutely nails it for resolution, and combined with the surface detail, I could not be happier...though to get that level of detail full disc would be nicer, an SF70 is not in budget right now.

I guess my images also show this, so it's not just idle speculation, I post up images with it all the time, and let anyone and everyone have a look through it at events.

Etalons on the PST are variable, whilst this may be coatings etc, I can only vouch for using 4 different PST's in a side by side, and keeping just the one, which was clearly head and shoulders better than the others.. The Vixen A80/C-ERF/PST/BF10 combination images like a dream (evidence online!) and visually, well just ask anyone who has looked through it... at SGL5/SSP or SGL imaging workshop day (brief sadly due to clouds)

I for one am NOT surprised by the LS35/PST shootout results... if it's a good PST that is...

£300 etalon it is, but you get the odd "perfect" one (Brian's data on that 0.65A giving 0.75A at F10 would seem about right)

Interesting roundup anyway...

What I also found interesting is the comparison between Pete's 0.5A DS SF70 and the SV50 I have which is single stack. Spoke at length to Ken at Solarscope yesterday and his words were "the figure on your SV50 and etalon were exceptionally good... I knew that at the time".

Nice to know..

Edited June 30, 2010 by NickH

[NickH]

For the record I have now used 7 Lunt LS50's and 60's and only 1 of them has even remotely impressed me in any way shape or form, most of them falling apart at high mag...Stephen Green's is the one which so far held up...and held up very well, and all have been tried with exactly the same kit...Lumenera Skynyx cams and Televue powermates

To be fair as well, I have just had an SV50 sent back for a tweak on the objective, as it wasn't as good as the other three on hand (60s and 50s), Ken's sorting it out though..

[GazOC]

Ken/ Peter,

So you need a donor scope with a focal length that will give you f10 given the aperture of your ERF?

[NickH]

Gaz

Get the Vixen A80... trust me.. for £100 there aint much to touch it, with the Baader D-ERF

[GazOC]

Cheers Nick, that scope does seem to be the best bet. The horse has already bolted for me though, I had first light yesterday with my PST 77 using an ED100 as a donor scope (runs at f11.6 so the f10 issue shouldn't be problem) and an old Lumicon ERF I got off that 1.5 Ang system they sold a while back.

Early signs look good. I'm seeing the proms and granuation easily but other surface detail (except sunspots obviously) are still escaping me at the moment. I'm not sure if the kit needs adjusting or my fledgling solar observing skills arn't up to scratch yet.

[NickH]

Gaz, are you coming to SSP? If so I will gladly give it a once over? (and that applies to any other PST mods at SSP)...