6" f5 Petzval refractor review.

[GazOC]

I've had my new (to me) 152mm f5 Petzval refractor out for the last 3 nights, once on a side by side plate with a 150mm f5 refractor. The scope is sold under the name Bresser Messier and AstroZap, its collimatable, stands at just over 3 ft tall (about the same length as a 150mm f6), weighs in at around 10kg and comes with a smooth and solid 4" focuser. The scope was bought from Skylight telescopes and arrived quickly, well packaged and included a free RDF.

The front lens is f10 with a reducing doublet in the focsuer to give a final figure of f5 for the scope. It's a damn sight bigger than the Skywatcher 150mm f5 in every respect and while the Skywatcher would be happy on a EQ5/ CG5 type mount, IMHO the Petzval would need at least a HEQ5/ Sirius and maybe even a EQ6/ Atlas to be really steady.

As the Moon was gibbous and washing out most of the sky I restricted myself to a quick star test, the Moon and Saturn. The star test showed the optics were well aligned, which was quite a relief after recieving a f5 Petzval through the post. It also showed very slight astigmatism which is n't enough to be a concern at the moment but which I'll try to nail down at a later date.

In comparision with the Skywatcher, the views where pretty similar on Saturn up to around x150 but after that the Petzval stood up a lot better, right up to X400 although it was 'empty magnification' after x350, which is still pretty impressive. The CA is slightly better controlled than the Skywatcher but still very obviously there, I'd have liked to have a 6" f8 for comparision, its been a few years since I owned a f8 but the two scopes are pretty close for controlling CA unless my memory is playing tricks. At high magnifications on Saturn the image was a lot brighter and crisper in the Petzval than the Skywatcher, I'm not sure if this is due to the CA, the longer focal ratio of the primary or the rumour that the 150mm f5 is stopped down, whichever it is, the difference is easily seen.

At first look I'm pretty happy with the scope, its a marked improvement over my Skywatcher the only real downside is the size of the scope, its heavier than a 6" f8 and longer than a 6" f5, but as it combines the best attributes of the two scopes maybe thats understandable??

The pros:

Decent 4" R&P focuser

Better colour correction than a 'normal' f5

Good at high powers

Two scopes in one (widefield and decent planetary)

Smaller than a 6" f8 but with comparable (?) performance

The Cons:

Pretty big all around

For low power widefield is the extra size worth it over a Skywatcher f5?

The dew shield is too short IMHO

[blinky]

Any piccies?

Nice review BTW

[Whippy]

Nice one Gaz, sounds pretty good to me .

Tony..

[MartinB]

Great objective report Gaz, interesting to hear how the petzval design performed

[GazOC]

Cheers Martin, I'll post some pics later this week. The Petzval design doesn't seem to work any miracles but having used the scope over 4 nights now its a definate and easy to see improvement over the 150mm f5.

[John]

Thanks for the report Gaz - as a refractor fan it's interesting to read about the performace of these more novel designs .

I think the Tele Vue Renaissance, Genesis and NP101 and some of the Vixens use a Petzval design if I recall. A nice flat field was one of the benefits that those companies claimed for the design.

John

[jgroub]

Great review.  You are convincing me to buy this one over the similar Explore Scientific AR152 f/6.5.  I didn't know that the objective lenses were f/10; that should go a ways in holding the CA down to "acceptable" levels.  (Which depends on what an individual observer considers acceptable.)  Thanks for the info.