Forgot Password
Pentax Camera Forums Home
 
Log in or register to remove ads.

Showing results 1 to 25 of 38 Search:
Forum: Sold Items 01-18-2020, 07:42 AM  
For Sale - Sold: SOLD Sigma DG 50-500 F4.5-6.3 APO HSM (OS)
Posted By MalcS
Replies: 8
Views: 1,986
PM sent... ;)
Forum: Pentax Medium Format 01-17-2020, 05:19 AM  
645 lens on K mount with 1.4 TC
Posted By MalcS
Replies: 9
Views: 807
Thanks for the info. I’m hoping to use this lens mostly for rocket launches, both here in VA (yes, we have rockets to the ISS!) and FL, where distance to rocket is on the order of 2-10 miles depending. Focusing shouldn’t really be an issue at that distance hopefully, and auto exposure, (which is not available with this lens of course using a K body) may not be that helpful anyway as when the rocket lights the exposure changes dramatically, so probably best to pre-guess exposure. Hours of waiting followed by 30 secs of frantic panic kinda sums it all up!

Lens coming from Japan, looks to be about as mint as can be, doesn’t even have scratches on the bottom of the tripod foot(!) and has both regular and polarizer filter holders, plus filters, caps, case, etc.

Meantime, here’s a few of the Antares Cygnus 12 leaving VA for the ISS from November, 300mm DA*: I’m sure they could be processed better... :) Distance about 2 miles, which is as close as you can be. Mirage was a problem, even though it was pretty cold.
Forum: Pentax Medium Format 01-15-2020, 04:58 PM  
645 lens on K mount with 1.4 TC
Posted By MalcS
Replies: 9
Views: 807
Thanks for going to the trouble and posting those.

I just picked up a good 645 1.4x for $50 from Japan and will probably get a 645 2x if only to ‘have the set’ :) Both seem dirt cheap on eBay considering the size of the glass elements and the bomb proof construction. Mechanically speaking the coupling between 645 components seems stronger than the K mount coupling.

BTW, if you don’t mind, what is the length of the tripod foot on the 645 600, and what is the size of the tripod threads (lens not here yet...need to get a plate for it), in pics it looks like 3/8 with a 1/4 insert reducer, or maybe it’s straight 1/4?

Thanks!
Forum: Pentax SLR Lens Discussion 01-09-2020, 04:22 PM  
Takumar/Super-Multi-Coated Takumar 500mm F4.5 VS. 500mm Mirror Lens
Posted By MalcS
Replies: 25
Views: 2,702
Indeed, keeps it simple and no need for a hyper expensive image degrading optical solution.
Forum: Pentax SLR Lens Discussion 01-09-2020, 09:01 AM  
Takumar/Super-Multi-Coated Takumar 500mm F4.5 VS. 500mm Mirror Lens
Posted By MalcS
Replies: 25
Views: 2,702
Mirror lenses are quite similar to some astronomical telescopes, namely Schmidt Cassegrains, and Maksutovs.

The first Ďproblemí they have is they are quite obstructed. The central obstruction is maybe 35-40%, and causes a reduction in contrast.
The second problem is that their aperture to focal length ratio is usually quite high, as in F8 or worse, which makes focusing difficult, and results in longer exposure times, which can be problematic due to long focal length (ie vibration/shake). The aperture is also fixed.
The third problem is that for economy of manufacture, the mirrors are made with a spherical figure, rather than parabolic, which leads to spherical abberations. The front glass element is supposed to correct for that, but...with varying success.
Lastly, in camera lens configuration there are additional lenses in the construction that donít appear in telescopes at all, to make the image is right side up and correct left to right as well, and hopefully bringing the image to focus over the entire area of the film or image sensor (flat field).

As an aside, a photographic Schmidt cassegrain telescope known as a Schmidt camera had an image plane so curved that the film (back in the day) had to be fitted to a curved film holder in order that the entire image be in focus.

At the end of the day, mirror lenses are a compromise in many ways, and the price is generally very low, so you know something has to give. I would expect the takumar to be superior in almost every way, though it will be prone to chromatic aberration (color fringing) due to the age of its design and no ED elements, and itís length makes it susceptible to vibration/shake unless well supported.

Just my $0.02...
Forum: Pentax SLR Lens Discussion 01-07-2020, 05:08 AM  
What is this fog-like looking on my lens?
Posted By MalcS
Replies: 10
Views: 1,412
There is no diagram of that lens in the reviews.

Itís difficult to tell. I have a cemented pair with fog that is balsam separation, looks almost like Ďcrystalsí between the elementsí but from a distance it looks like whitish fog.

Did the front element come out by itself, or did you find two pieces of glass mounted in a metal Ďcellí?
If 2 elements mounted together in a cell, itís difficult to tell if they are cemented without disassembly. It is highly likely that the cell has a drop or two of lacquer on the threads that holds the top ring of the cell in place. You can use nail polish remover (acetone) to dissolve the lacquer and remove the ring, allowing the elements to be taken out of the cell, at which point you will know if they are cemented or not. I stand the cell on its side, and using a hyperdermic syringe and needle, run a little acetone around the edge and leave it for a few minutes before trying to unscrew the ring.

I got a set of rubber/silicone tools from amazon that allow you to remove rings in lenses and cells using friction (once the lacquer is dissolved). It it possible to use a lens wrench too, but be careful as the metal tool can scratch glass if you slip.

If there are two loose elements, make sure you know the order and direction (up/down) they were in. If possible, keep them together and make a mark with a pencil across the edges of both so you can put them back exactly as they were.

I would use some rubbing alcohol or even acetone to clean the glass and a microfiber cloth. Reassemble. Done.

If they are cemented, itís more of a problem...
Forum: Pentax Forums Giveaways 01-06-2020, 09:45 PM  
PentaxForums 100 Year Giveaway - December/January - General Raffle Entry Thread
Posted By MalcS
Replies: 385
Views: 13,296
Count me in too....
Forum: Pentax SLR Lens Discussion 01-06-2020, 06:49 PM  
Pentax - A 400mm F2.8 insanity.... advice
Posted By MalcS
Replies: 31
Views: 2,070
The crack is actually in the second element, which I think is ED glass if the diagram in the forum lens reviews section is correct.

Judging by the state of the ring that holds the front element in place (and the others inside the lens), I would say there has been no attempt to take it apart since it was made (lens spanners / wrenches generally leave a mark in the soft aluminum rings, knock the flat black paint off etc, no sign of that at all). Unless someone had a replacement element, I’m not sure it would be at all advisable to take it apart, it could only make things worse.

It may have been ok as is, the aperture blades might have been an easy fix, but I decided not to take a chance on it, and sent it back today.

As has been pointed out, it could have got worse if the glass moved at all, fixing it properly (assuming Pentax even have the damaged element, they may not) would have been really expensive I’m sure, and would have exceeded the used value of a similar lens. That said, it might have been just fine ‘as-is’ for the next 20 years...and the crack may have minimal to zero effect on images, it is maybe 5-8mm from the edge.

At a massive discount to a few hundred bucks, it might have been worth the risk, but I decided not to even ask them if they’d consider it.

Anyone who’s interested in making them an offer (I don’t know what they’d be open to) could contact Josh at Calagaz Photo in Pensacola, FL, you might get lucky, I have no idea, but I can’t imagine what else they’d do with the thing in its current state. It’s missing it’s rear filter, but I imagine any 49mm UV or clear filter would fit the holder, which is present.

I would also say I don’t think Calagaz really knew. Unless you’re looking closely, or with a flashlight, the crack is not super apparent (but they should have seen it). Likewise, the aperture stickiness could have been missed if you just operated it once or twice, it’s a bit sporadic, but it is a problem they should have seen. They sent me a return label right away.
Forum: Pentax Medium Format 01-05-2020, 11:17 PM  
645 lens on K mount with 1.4 TC
Posted By MalcS
Replies: 9
Views: 807
When using a 645 lens on K mount (say the 600mm ED IF f5.6) using the Pentax 645->K adapter, which would work better on an apsc camera (K3 or K5):

a) the 645 version 1.4 teleconverter mounted to the lens, before the K adapter?
Or
b) the well regarded, (almost magical... ) 35mm (K mount) 1.4x-l converter mounted after the K adapter?

Anyone tried (b)? I can’t think why it wouldn’t work... ;)

I suppose if mechanics are a consideration, perhaps the mechanical connection between 645 lens and 645 converter might be stronger(?)
Forum: Pentax SLR Lens Discussion 01-05-2020, 02:46 PM  
Pentax - A 400mm F2.8 insanity.... advice
Posted By MalcS
Replies: 31
Views: 2,070
Agreed on all points! At this point Iím 99% on sending back and forgetting about it, lest it become another box in the basement...

SCTís - thatís an idea. I have an 8Ē Celestron in a gps/computerized fork mount, so I know the ins and outs. I suppose a small (relatively) refractor might be a possibility too, though Iíve never used one for terrestrial, but APOs tend to be up there in price, and achromats are the definition of CA. Iíve bought from High Point before.
Forum: Pentax SLR Lens Discussion 01-05-2020, 02:38 PM  
Pentax - A 400mm F2.8 insanity.... advice
Posted By MalcS
Replies: 31
Views: 2,070
Havenít seen one used recently, but will certainly keep an eye out!
Forum: Pentax SLR Lens Discussion 01-05-2020, 11:10 AM  
Pentax - A 400mm F2.8 insanity.... advice
Posted By MalcS
Replies: 31
Views: 2,070
Added to database.
Forum: Pentax SLR Lens Discussion 01-05-2020, 08:30 AM  
Pentax - A 400mm F2.8 insanity.... advice
Posted By MalcS
Replies: 31
Views: 2,070
Yes, looked for a A* 600. Saw one for a split second on that auction site, then it disappeared, now shows as completed / sold. Itís possible it didnít actually sell, may contact seller and see.

$2700 for the current DA 560 would be a deal!

Patience is key... :)
Forum: Pentax SLR Lens Discussion 01-05-2020, 08:13 AM  
Pentax - A 400mm F2.8 insanity.... advice
Posted By MalcS
Replies: 31
Views: 2,070
Actually, that is an excellent point I hadnít really considered, and 100% on target.

Out of interest, have you ever tried the 645 600 on a K mount camera? Stop down metering is a given, but they seem reasonably available in good/excellent shape compared to older 35mm lenses from the same era... reviews on here seem very good.

I recently gave my 645 film body and lenses to my niece for a university project, but kept the Pentax 645 -> K mount adapter...
Forum: Pentax SLR Lens Discussion 01-05-2020, 08:04 AM  
Pentax - A 400mm F2.8 insanity.... advice
Posted By MalcS
Replies: 31
Views: 2,070
Thanks for the sanity check!

Yes, it’s a lot of money for a lens with a crack. Seller and I didn’t know it was cracked though, so price paid was ostensibly for an uncracked one!

Not sure there’s any amount of $ partial refund that would convince me to keep it, as it could just turn into a paperweight at some point, assuming it isn’t now... That really was the decision at this point, but crazy to keep it at any price I think....

No idea how the crack occurred, only the original owner knows that for sure (bought from a dealer). No obvious hit on it, this thing weighs about 15lbs and is a little over a foot long, so I’m not sure a drop would even leave a mark.

Going to box it up, ship it back...
Forum: Pentax SLR Lens Discussion 01-05-2020, 06:16 AM  
Pentax - A 400mm F2.8 insanity.... advice
Posted By MalcS
Replies: 31
Views: 2,070
Just scored a 400mm F2.8, with a 1.7 AF teleconverter for what seemed to be a good price... described as ‘excellent’.

Lens arrived, had a real tree camo sticky backed vinyl covering, which I removed, revealing very nice condition white exterior, a few marks, but nice. Filter holder is there, has no filter, but could easily fit one, I think it may require one in place.

Aperture blades, which are accessible from the back, are sticky. Maybe some alcohol would fix, or send to KEH.

Glass is clear, focusing is reasonably smooth. Have not attempted to take a pic with it yet.

The BAD part....

There is a CRACK in the second element. It is basically a straight line crack about 1cm or so from the edge of the second element. Difficult to see at first glance, but it is there (and now that I see it, I can see it in the seller’s somewhat out of focus photo too). I guess they didn’t notice it.

Seller's pic attached, the crack is at 3-4 O'clock. Yeah, obvious now.... :)

I spoke to the seller yesterday, and I have a return label, so can get $$$ back on this ($2600) they seem reasonable at this point.

But... should I run like hell, send it back, cry for a bit and forget about it.

Or make some ridiculously low offer to just keep it?

It’s possible the crack could have little to no effect. It’s possible it might never move. It’s close to the edge of the lens, perhaps it doesn’t even intrude into the APSC field of view??? I know sigma say one of their lenses (bigma maybe) takes a 95mm filter, but you can use a step down ring to 86mm when shooting APSC, which got me thinking....

My use for this lens is for shooting rocket launches using my K3, which may be at a range of 2 miles to 10 miles distant. The attraction of this lens was that with the 1.7 AF tc I could get to equivalent of a 1020mm f4.7 approx, still have some autofocus ability, it would also work with the 1.4x-l and 2x-l converters, which are rated about as good as it gets for TCs, albeit manual focus.

Alternatively, get a Bigma 50-500, or even a Pentax 150-450, pocket the change and never look back. The DA 560 is too much $$$ for me I think.

I do have a DA*300 that I could put a 1.4 TC on and save a fortune. Not quite the same but...

I don’t really want to have a ‘stupidest thing I ever did’ story (either way!).

Thoughts?
Forum: Sold Items 12-25-2019, 04:50 AM  
For Sale - Sold: SOLD Sigma DG 50-500 F4.5-6.3 APO HSM (OS)
Posted By MalcS
Replies: 8
Views: 1,986
PM sent....
Forum: Visitors' Center 10-15-2019, 10:50 PM  
pentax ist D won't power on
Posted By MalcS
Replies: 18
Views: 2,163
Had the same problem with my ist*D with a new set of lithium AAs. The fix was to put the AAs in a flash, charge it up, fire once, and then put the batteries back in the camera, after which it worked fine from then on. Not sure if this is a fault with the camera or what exactly, but it seems it doesn’t draw enough power to ‘wake up’ the new lithiums initially. If you don’t have a flash, any device that draws a bit of power should do the trick (assuming the problem you are having is the same). Wierd...
Forum: Sold Items 09-27-2019, 11:17 AM  
For Sale - Sold: SMC Pentax-DA 50-200mm F4-5.6 ED WR
Posted By MalcS
Replies: 0
Views: 556
PentaxForums.com Marketplace Listing

Item for Sale
For Sale: SMC Pentax-DA 50-200mm F4-5.6 ED WR

Asking Price
90.00 USD

Item Location
Virginia (United States)

Item Description
SMC Pentax-DA 50-200mm F4-5.6 ED WR in excellent condition, with both original caps, Pentax hood, box, bubble wrap, papers.

Lens shows next to no signs of use, looks like new.

Selling due to other aquisition(s) with a similar focal range... ;)

Are you the original owner of the item being sold?
No

Are you selling or trading this item?
Selling

Item Condition (Key)
Used
Excellent

Shipping Destinations
United States

Shipping Charge
10

Shipping Services
USPS Priority Mail

Accepted Payment Types
PayPal

Return Policy & Additional Details
7 day return at buyers cost if not as described.

Please send me a private message if interested in the item!
Forum: Pentax SLR Lens Discussion 09-14-2019, 08:26 AM  
Hacking the 60-250 SDM/screwdrive fix
Posted By MalcS
Replies: 7
Views: 1,171
I agree, it’s like trying to figure out what’s in Pandora’s box without being able to open it.

However, for all I/we know the camera downloads the entire rom at once, and then uses that, which would still cause consistent failure. I guess....
Forum: Pentax SLR Lens Discussion 09-14-2019, 06:34 AM  
Hacking the 60-250 SDM/screwdrive fix
Posted By MalcS
Replies: 7
Views: 1,171
Ok, probably everyone knows that the da* 60-250 cannot be converted to screwdrive when the SDM fails, as the hack that works on the other lenses does not work on the 60-250.

But why?

I have a theory, (for which there may only be a smidge of supporting evidence) as to why it doesnít work.

I donít actually have a 60-250, but itís been bugging me....

Observations:

a) The 60-250 has the biggest zoom range of all the SDM/screwdrive lenses.
b) There are multiple records in the firmware that require the C0 -> 80 change in the different lenses. It seems to be that the camera can/will/may read these records from the lens at any time when the focus or zoom rings move. This data may include current zoom position, and current focus distance.
c) The amount of filled in data in the firmware seems to vary from lens to lens (for example the da* 300) has much less, but it is not a zoom, so perhaps not surprising.
d) When applying the hack to the 60-250 it kinda/sorta works until the focus changes or perhaps the zoom changes, which implies a non modded record was read from the lens.

Theory:

The fix doesnít work because the rom table in the 60-250 is larger than the camera debug options can read or write. When the fix is applied, some, but not all of the rom is modified. When the 60-250 lens is modded and used, the camera quickly reads in a non modified record and switches back to sdm, which causes failure.

The fix:

Somebody needs to modify the firmware to read and write more than 2k bytes of rom, which is how much the debug options are currently able to read and write to/from the lens, 4kb would be good I think.

Or, perhaps easier, modify the interactive lens rom editor (another debug menu option). Currently this debug option allows changes to be made only to the first 1kb of the rom (highest allowed offset 0x03FF) it should ideally be perhaps 0x0FFF (4kb). It is notable that the rom sd card read/write routines can handle 2kb of rom, but the interactive editor is restricted to 1kb, which really highlights the fact that the lens debug options are old code that may not handle changes made to lens rom size over time. Plus they took them out altogether in the later cameras.

Regrettably this is only a theory, it would require someone quite skilled to even find out if the reasoning is valid.

I have seen some old Ďhackerí threads, are any of these people still around?

If the theory is correct, the community would only need one modified camera to fix 60-250 lenses... It may not be correct, however...
Forum: Sold Items 09-01-2019, 05:47 AM  
For Sale - Sold: HD Pentax DA 1.4 AF Rear Converter $275, Reduced to $250.00 plus shipping
Posted By MalcS
Replies: 3
Views: 1,097
PM sent....
Forum: Sold Items 07-09-2019, 07:25 PM  
For Sale - Sold: Sigma 8-16 mm F/4.5-5.6 DC HSM
Posted By MalcS
Replies: 2
Views: 897
PM sent
Forum: Pentax Price Watch 05-08-2014, 06:27 AM  
New Pentax Q10 for $159.99 free shipping
Posted By MalcS
Replies: 18
Views: 3,774
I put in Australia as the shipping option, and it looked good to go with a $30 shipping charge(?)
Forum: Sold Items 06-14-2013, 10:50 PM  
For Sale - Sold: BNIB Pentax K-01 (Black) Kit with 40mm f2.8
Posted By MalcS
Replies: 2
Views: 1,110
** sold **
Search took 0.00 seconds | Showing results 1 to 25 of 38

 
Forum Jump


All times are GMT -7. The time now is 08:56 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top