Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
11-03-2010, 11:14 AM   #1
Inactive Account




Join Date: Nov 2010
Location: Central Florida
Posts: 16
F-stop question

First of all, hello everyone. I actually own a Chinon CP-7m but it takes a Pentax K-Mount lens so I hope it is okay to post in here about my camera...

I actually bought a CP-7m back in 1987 when they first came out...with everything, lenses, flash, case, body, etc I paid nearly $1000.00. Used it for a few years and
then it got "lost" when I got divorced....or so she said..

Anyhow..I just picked this CP-7m up off E-bay ($50.00) and had a question. I have discovered that there is a problem with the hot-shoe for the flash. The camera does not recognize the flash as far as the onboard computer goes. No red light saying the flash is ready and no change in shutter speed that should happen when I add the flash. But, the flash DOES work...so I figured out I can manually set the shutter speed for the flash. But, what about the f-stop?

Generally, acording to the manual that came with the camera, when using the flash the shutter speed is 125. And in auto mode using the flash I should keep the f-stop at 8.0. But I am in manual mode to force the faster shutter speed. Is there a table or something for distance that I can use for the recommended f-stop? And would 8.0 be a good "general for most pictures" f-stop setting?

Any help would be appreciated.


Last edited by webkrawler; 11-03-2010 at 11:32 AM. Reason: Forgot something
11-03-2010, 11:33 AM   #2
Veteran Member
Nesster's Avatar

Join Date: Oct 2006
Location: NJ USA
Photos: Gallery
Posts: 13,047
You don't mention what flash this is. The flash needs to be dedicated or support the dedicated scheme of the CP-7m, in order for the automation to work. You still get the hot shoe triggering, however, as you say.

What you need to do is to figure out which flavor of dedication the Chinon has, and then find a flash that supports the same. E.g. Vivitar made different models for different sets of cameras, 3 brands per model supported. Google is your friend

To use a flash in auto-Thyristor mode (i.e. the flash uses its own sensor): there are usually 2 auto power settings. You set the film speed on the flash, select the power setting, and read off the f/stop from the flash setting mechanism. Simply set your lens to that stop and your shutter to at most the max sync speed, and you're good to go.

You shouldn't use a speed > 1/125 if this is the max sync speed on the camera.

If your flash doesn't have auto modes, then you're going to calculate things based on distance and guide number - google 'flash guide number' and you should get much advice. Back in the day I pre-calculated a table based on focus zones for a flash cube flash and stuck that on the flash.
11-03-2010, 11:48 AM   #3
Pentaxian




Join Date: Sep 2007
Location: Bay Village, Ohio USA
Posts: 1,037
QuoteOriginally posted by webkrawler Quote
Generally, acording to the manual that came with the camera, when using the flash the shutter speed is 125. And in auto mode using the flash I should keep the f-stop at 8.0. But I am in manual mode to force the faster shutter speed. Is there a table or something for distance that I can use for the recommended f-stop? And would 8.0 be a good "general for most pictures" f-stop setting?

Any help would be appreciated.

You can't set the shutter speed above a certain, camera-dependent limit. This is called the maximum sync speed, or X-speed. The focal plane shutter on most SLR's is composed of two curtains or metal blades. When the shutter is tripped, the leading, or opening curtain opens. After a brief period of time, depending on the shutter speed chosen, the trailing or closing curtain closes.

If the manual recommends using 1/125 second, that probably means that that is the fastest shutter speed at which the film frame is completely exposed. At faster shutter speeds, the trainling curtain begins closing BEFORE the leading curtain is fully open. This results in a moving slit that travels across the frame. The faster the shutter speed, the smaller the slit.

The duration of an electronic flash is usually, at most, about 1/1,000 second. So-called "Auto" flashes vary the duration to as little as 1/30,000 or 1/50,000 second. For this reason, the camera's shutter speed is largely irrelevant. But, if you set the shutter speed too fast, the entire frame will not be exposed for the tiny fraction of a second that the flash is on. The result is a dark band at one side (or top/bottom, if you have a vertical travel shutter) where the shutter blade blocked the frame. For electronic flash to work, the entire frame must be open.

It would sure help to know the make/model of the flash you are using. As nesstor said, unless the flash is specifically "dedicated" to your camera, the two won't commnicate and the automation won't work.
11-03-2010, 12:08 PM   #4
Inactive Account




Join Date: Nov 2010
Location: Central Florida
Posts: 16
Original Poster
The make and model of the flash is Chinon S-250 Zoom. The Zoom is printed under the S-250 so not sure if that is really part of the proper name or not.

Thanx for the input so far. There does not seem to be anything wrong with the hot-shoe itself from just looking at it. It is not loose and makes a nice secure bind with the flash and seats perfectly.

The flash also looks in excellent shape...

In the manual it stated --

The flash ready LED (red) and 1/125 sec. LED (green) in viewfinder will light up.

....when the flash is properly mounted and turned ON in AUTO mode and the camera is in Program mode. So, this is where I found the information for the 125 shutter speed. I think I also read the guide number is 100??

and the red LED in the viewfinder never lights up when the flash is attached and on. From what I have seen, almost all CP-7m's on Ebay that are sold with a flash are sold with this same S-250 flash. So, i would think it would be compatible.

I very much a novice but appreciate the help!!


Last edited by webkrawler; 11-03-2010 at 12:19 PM.
11-03-2010, 06:41 PM   #5
Pentaxian




Join Date: Sep 2007
Location: Bay Village, Ohio USA
Posts: 1,037
I looked up the manual for your flash. It is, indeed, dedicated to your camera.

I noticed that the flash has both an auto mode and a manual mode, controlled by a switch on the back. Is it possible that you have the flash in manual mode? That might, in effect, disable the automation. This seems unlikely, though, because I would think that the ready light would still work.

Have your tried fresh batteries in the flash? I have a Vivitar 283 flash, in which the ready light will not turn on with partially used batteries, even though the flash will charge up and fire.

A basic hotshoe has only two connectors. There is a center pin and a contact on the side of the shoe. These two connections are all that is necessary to fire the flash. Automation is handled by additional, typically smaller pins that surround the center pin. Make sure that these additional contacts match up on the camera and flash, and that none of them are damaged.

Paul
11-03-2010, 07:09 PM   #6
Inactive Account




Join Date: Nov 2010
Location: Central Florida
Posts: 16
Original Poster
Hey there, thanx for the reply.

Yes, I have tried the manual and auto switch...it did not make any difference.

The batteries I am using are new...but they still could be old...the
CVS where I live ALWAYS has old sometimes dead batteries on their
shelves for sale. I stopped buying batteries from them. These batteries
were purchased somewhere else where I would not expect to find
stale batteries...but it's possible.

I'll buy another package of batteries..this time Energizers as these
were the store brand's alkaline batteries.

I couple of days ago I bought a 2nd CP-7m on E-bay and it should be
here in a day or so....I figured it would be a backup...when it comes in
I can use it with the flash as well to see if the problem might be caused by the flash...

Thanx again for your input...
11-04-2010, 05:33 AM   #7
Veteran Member
Nesster's Avatar

Join Date: Oct 2006
Location: NJ USA
Photos: Gallery
Posts: 13,047
Try cleaning the contacts on both hot shoe and the flash. Also try gently rocking the flash in the shoe, in case the electrical bits aren't lining up correctly - gently as you don't want to break anything.
11-04-2010, 07:26 AM   #8
Moderator
Site Supporter
Blue's Avatar

Join Date: Jun 2008
Location: Florida Hill Country
Photos: Gallery | Albums
Posts: 17,197
I bought one of these in 1987 as well and I still have it. The only issue I have about the camera is the dedicated flash aspect. There are only 2 Chinon flash models that will work in the dedicated mode and 1 or 2 SunPack flashes that will work in the dedicated mode on the CP-7m. Its to the auto flash mode on the flash or manual mode. Unfortunately this means you lose the fasted flash sync. That said this is an excellent body and can actually us M and k lenses in auto aperture mode without the need for the A setting on the aperture ring. This is the only k-mount body made by anyone that can do that.

11-04-2010, 08:06 AM   #9
Moderator
Site Supporter
Blue's Avatar

Join Date: Jun 2008
Location: Florida Hill Country
Photos: Gallery | Albums
Posts: 17,197
QuoteOriginally posted by webkrawler Quote
The make and model of the flash is Chinon S-250 Zoom. The Zoom is printed under the S-250 so not sure if that is really part of the proper name or not.

Thanx for the input so far. There does not seem to be anything wrong with the hot-shoe itself from just looking at it. It is not loose and makes a nice secure bind with the flash and seats perfectly.

The flash also looks in excellent shape...

In the manual it stated --

The flash ready LED (red) and 1/125 sec. LED (green) in viewfinder will light up.

....when the flash is properly mounted and turned ON in AUTO mode and the camera is in Program mode. So, this is where I found the information for the 125 shutter speed. I think I also read the guide number is 100??

and the red LED in the viewfinder never lights up when the flash is attached and on. From what I have seen, almost all CP-7m's on Ebay that are sold with a flash are sold with this same S-250 flash. So, i would think it would be compatible.

I very much a novice but appreciate the help!!
Your camera needs to be in either the Auto Mode or manual mode. The sync speed when the Flash is operating the camera in dedicated mode is 1/100. When in the Auto or Manual mode the flash will automatically put the camera at 1/100 but it won't do it in the Program mode.

The Chinon S-280 will work in dedicated mode (NOT the AF-S-280 which is for the AF body)

I used the SunPack 2000DZ with my body body the flash has died on me.

The S-250 is supposed to work with it.

Chinon S-250 Flash instruction manual, user manual, free instruction manual, pdf manuals
11-04-2010, 07:56 PM   #10
Inactive Account




Join Date: Nov 2010
Location: Central Florida
Posts: 16
Original Poster
Well, the flash DOES work..I mean, I can mount the flash, take a picture, and the flash goes off when I take a picture...BUT...whether the flash is in auto or manual mode, the camera does not light up the LED that tells me the flash is ready (when the flash itself tells me its ready) AND the camera acts like there is no flash attached..that means it shoots the picture at a shutter speed, depending on the ambient light, at 1/4 or 1/8 speed. I am assuming this is bad as when I take the flash completely off the camera and attempt the identical shot, it also takes the picture at 1/4 or 1/8 shutter speed.

I did not get around to getting new batteries today but I plan to pick some up..and I will try to clean the contacts but they looked pretty clean when I examined them...

Thanx again...I'll keep you guys informed...
11-07-2010, 12:54 PM   #11
Inactive Account




Join Date: Nov 2010
Location: Central Florida
Posts: 16
Original Poster
Well, I tried new Energizers from a busy camera store (busiest one in town) so I can't imagine the batteries being stale. The flash is still not recognized by
the camera...

I finally found some information from some Chinon manal that says
I can use a non-dedicated flash by using manual mode and a
shutter speed of 1/60. The f-stop also has to set manually.

So, I took the camera to my best friends rehearsal dinner with the
flash I have now sent the roll to Snapfish to develop.

We'll see how well it turned out. I still don't have the other camera
body in yet to test the flash I have with it.
11-08-2010, 02:46 PM   #12
Inactive Account




Join Date: Nov 2010
Location: Central Florida
Posts: 16
Original Poster
Well, I got the 2nd CP-7M body in and the S-250 flash that I have WORKS on that camera in Program mode (it recognizes it)...so the problem is with the other body and not with the flash...

I don't think it pays to fix the hot shoe on that body...

Well, now I am going to run a couple of rolls through the 2nd body to see how it performs..

**update** Actually it did not work. The camera "seemed" to recoginze it but when I started actually
using it the flash failed to go off in Automatic mode** This 2nd camera has additional problems the first one
does not have like the LCD resets the film frame counter back to "0" in the middle of a roll of film and a couple
of times the shutter got "stuck" after taking a picture.**

Last edited by webkrawler; 12-02-2010 at 05:41 PM.
12-02-2010, 05:38 PM   #13
Inactive Account




Join Date: Nov 2010
Location: Central Florida
Posts: 16
Original Poster
Final post

I thought I would make one final post as I started the thread...

I spent another $25 on E-bay for a dedicated Chinar flash that the
owner guaranteed worked.

I now have it and what do you know...the flash is being recognized by
the camera...

This means that there is a problem with the original flash...

And to think I thought about sending the camera in and pay
$150.00 to get the hot shoe or whatever the problem was repaired.

Better deal at $25
12-03-2010, 08:32 AM   #14
Moderator
Site Supporter
Blue's Avatar

Join Date: Jun 2008
Location: Florida Hill Country
Photos: Gallery | Albums
Posts: 17,197
QuoteOriginally posted by webkrawler Quote
I thought I would make one final post as I started the thread...

I spent another $25 on E-bay for a dedicated Chinar flash that the
owner guaranteed worked.

I now have it and what do you know...the flash is being recognized by
the camera...

This means that there is a problem with the original flash...

And to think I thought about sending the camera in and pay
$150.00 to get the hot shoe or whatever the problem was repaired.

Better deal at $25
Glad to hear it. These are nice film bodies. It was my work horse for over 16 years. I figured the issue was in the flash itself.

Don't be a stranger on this site though.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
camera, f-stop, flash, mode, question, shutter
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
f stop question sealonsf Troubleshooting and Beginner Help 4 03-24-2010 07:46 AM
Lens F/stop Limitation Question seachunk2 Troubleshooting and Beginner Help 10 02-26-2010 07:27 AM
DOF and F-stop question. denhamcla Troubleshooting and Beginner Help 4 09-13-2009 11:51 AM
Somebody Stop Me!!! shutterpuppy Photographic Technique 1 02-12-2009 02:46 AM
I just cant stop... Igilligan Post Your Photos! 18 10-25-2008 04:52 PM



All times are GMT -7. The time now is 03:45 AM. | 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